java菜鸟教程学习（完整版）

一.Java 字符串

1.Java 实例 – 字符串比较

public class StringCompareEmp{
    
    
   public static void main(String args[]){
    
    
      String str = "Hello World";
      String anotherString = "hello world";
      Object objStr = str;
 
      System.out.println( str.compareTo(anotherString) );
      System.out.println( str.compareToIgnoreCase(anotherString) );  //忽略大小写
      System.out.println( str.compareTo(objStr.toString()));
   }
}

2.Java 实例 - 查找字符串最后一次出现的位置

public class SearchlastString {
    
    
   public static void main(String[] args) {
    
    
      String strOrig = "Hello world ,Hello Runoob";
      int lastIndex = strOrig.lastIndexOf("Runoob");
      if(lastIndex == - 1){
    
    
         System.out.println("没有找到字符串 Runoob");
      }else{
    
    
         System.out.println("Runoob 字符串最后出现的位置： "+ lastIndex);
      }
   }
}

3.Java 实例 - 删除字符串中的一个字符

public class Main {
    
    
   public static void main(String args[]) {
    
    
      String str = "this is Java";
      System.out.println(removeCharAt(str, 3));
   }
   public static String removeCharAt(String s, int pos) {
    
    
      return s.substring(0, pos) + s.substring(pos + 1);
   }
}

4.Java 实例 - 字符串替换

public class StringReplaceEmp{
    
    
   public static void main(String args[]){
    
    
      String str="Hello World";
      System.out.println( str.replace( 'H','W' ) );
      System.out.println( str.replaceFirst("He", "Wa") );
      System.out.println( str.replaceAll("He", "Ha") );
   }
}

5.Java 实例 - 字符串反转

public class StringReverseExample{
    
    
   public static void main(String[] args){
    
    
      String string="runoob";
      String reverse = new StringBuffer(string).reverse().toString();
      System.out.println("字符串反转前:"+string);
      System.out.println("字符串反转后:"+reverse);
   }
}

6.Java 实例 - 字符串查找

public class SearchStringEmp {
    
    
   public static void main(String[] args) {
    
    
      String strOrig = "Google Runoob Taobao";
      int intIndex = strOrig.indexOf("Runoob");
      if(intIndex == - 1){
    
    
         System.out.println("没有找到字符串 Runoob");
      }else{
    
    
         System.out.println("Runoob 字符串位置 " + intIndex);
      }
   }
}

7.Java 实例 - 字符串分割

public class JavaStringSplitEmp {
    
    
   public static void main(String args[]){
    
    
      
      String str = "www-runoob-com";
      String[] temp;
      String delimeter = "-";  // 指定分割字符
      temp = str.split(delimeter); // 分割字符串
      // 普通 for 循环
      for(int i =0; i < temp.length ; i++){
    
    
         System.out.println(temp[i]);
         System.out.println("");
      }
 
      System.out.println("------java for each循环输出的方法-----");
      String str1 = "www.runoob.com";
      String[] temp1;
      String delimeter1 = "\\.";  // 指定分割字符， . 号需要转义
      temp1 = str1.split(delimeter1); // 分割字符串
      for(String x :  temp1){
    
    
         System.out.println(x);
         System.out.println("");
      }
   }
}

8.Java 实例 - 字符串分割(StringTokenizer)

import java.util.StringTokenizer;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
 
        String str = "This is String , split by StringTokenizer, created by runoob";
        StringTokenizer st = new StringTokenizer(str);
 
        System.out.println("----- 通过空格分隔 ------");
        while (st.hasMoreElements()) {
    
    
            System.out.println(st.nextElement());
        }
 
        System.out.println("----- 通过逗号分隔 ------");
        StringTokenizer st2 = new StringTokenizer(str, ",");
 
        while (st2.hasMoreElements()) {
    
    
            System.out.println(st2.nextElement());
        }
    }
}

9.Java 实例 - 字符串小写转大写

public class StringToUpperCaseEmp {
    
    
    public static void main(String[] args) {
    
    
        String str = "string runoob";
        String strUpper = str.toUpperCase();
        System.out.println("原始字符串: " + str);
        System.out.println("转换为大写: " + strUpper);
    }
}

10.Java 实例 - 测试两个字符串区域是否相等

public class StringRegionMatch{
    
    
   public static void main(String[] args){
    
    
      String first_str = "Welcome to Microsoft";
      String second_str = "I work with microsoft";
      boolean match1 = first_str.
      regionMatches(11, second_str, 12, 9);
      boolean match2 = first_str.
      regionMatches(true, 11, second_str, 12, 9); //第一个参数 true 表示忽略大小写区别
      System.out.println("区分大小写返回值：" + match1);
      System.out.println("不区分大小写返回值：" + match2);
   }
}

11.Java 实例 - 字符串性能比较测试

public class StringComparePerformance{
    
    
   public static void main(String[] args){
    
          
      long startTime = System.currentTimeMillis();
      for(int i=0;i<50000;i++){
    
    
         String s1 = "hello";
         String s2 = "hello"; 
      }
      long endTime = System.currentTimeMillis();
      System.out.println("通过 String 关键词创建字符串" 
      + " : "+ (endTime - startTime) 
      + " 毫秒" );       
      long startTime1 = System.currentTimeMillis();
      for(int i=0;i<50000;i++){
    
    
         String s3 = new String("hello");
         String s4 = new String("hello");
      }
      long endTime1 = System.currentTimeMillis();
      System.out.println("通过 String 对象创建字符串" 
      + " : " + (endTime1 - startTime1)
      + " 毫秒");
   }
}

12.Java 实例 - 字符串优化

public class StringOptimization {
    
    
    public static void main(String[] args){
    
    
        String variables[] = new String[50000];      
        for( int i=0;i <50000;i++){
    
    
            variables[i] = "s"+i;
        }
        long startTime0 = System.currentTimeMillis();
        for(int i=0;i<50000;i++){
    
    
            variables[i] = "hello";
        }
        long endTime0 = System.currentTimeMillis();
        System.out.println("直接使用字符串： "+ (endTime0 - startTime0)  + " ms" );
        long startTime1 = System.currentTimeMillis();
            for(int i=0;i<50000;i++){
    
    
            variables[i] = new String("hello");
        }
        long endTime1 = System.currentTimeMillis();
        System.out.println("使用 new 关键字：" + (endTime1 - startTime1) + " ms");
        long startTime2 = System.currentTimeMillis();
        for(int i=0;i<50000;i++){
    
    
            variables[i] = new String("hello");
            variables[i] = variables[i].intern();          
        }
        long endTime2 = System.currentTimeMillis();
        System.out.println("使用字符串对象的 intern() 方法: " 
        + (endTime2 - startTime2)
        + " ms");
    }
}

13.Java 实例 - 字符串格式化

import java.util.*;
 
public class StringFormat {
    
    
    public static void main(String[] args){
    
    
        double e = Math.E;
        System.out.format("%f%n", e);
        System.out.format(Locale.CHINA  , "%-10.4f%n%n", e);  //指定本地为中国（CHINA）
    }
}

14.Java 实例 - 连接字符串

public class StringConcatenate {
    
    
    public static void main(String[] args){
    
    
        long startTime = System.currentTimeMillis();
        for(int i=0;i<5000;i++){
    
    
            String result = "This is"
            + "testing the"
            + "difference"+ "between"
            + "String"+ "and"+ "StringBuffer";
        }
        long endTime = System.currentTimeMillis();
        System.out.println("字符串连接" 
        + " - 使用 + 操作符 : " 
        + (endTime - startTime)+ " ms");
        long startTime1 = System.currentTimeMillis();
        for(int i=0;i<5000;i++){
    
    
            StringBuffer result = new StringBuffer();
            result.append("This is");
            result.append("testing the");
            result.append("difference");
            result.append("between");
            result.append("String");
            result.append("and");
            result.append("StringBuffer");
        }
        long endTime1 = System.currentTimeMillis();
        System.out.println("字符串连接" 
        + " - 使用 StringBuffer : "
        + (endTime1 - startTime1)+ " ms");
    }
}

二.Java 数组

1.Java 实例 – 数组排序及元素查找

import java.util.Arrays;
 
public class MainClass {
    
    
    public static void main(String args[]) throws Exception {
    
    
        int array[] = {
    
     2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
        Arrays.sort(array);
        printArray("数组排序结果为", array);
        int index = Arrays.binarySearch(array, 2);
        System.out.println("元素 2  在第 " + index + " 个位置");
    }
    private static void printArray(String message, int array[]) {
    
    
        System.out.println(message
        + ": [length: " + array.length + "]");
        for (int i = 0; i < array.length; i++) {
    
    
            if(i != 0){
    
    
                System.out.print(", ");
            }
            System.out.print(array[i]);
        }
        System.out.println();
    }
}

2.Java 实例 – 数组添加元素

import java.util.Arrays;
 
public class MainClass {
    
    
   public static void main(String args[]) throws Exception {
    
    
      int array[] = {
    
     2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
      Arrays.sort(array);
      printArray("数组排序", array);
      int index = Arrays.binarySearch(array, 1);
      System.out.println("元素 1 所在位置（负数为不存在）："
      + index);  
      int newIndex = -index - 1;
      array = insertElement(array, 1, newIndex);
      printArray("数组添加元素 1", array);
   }
   private static void printArray(String message, int array[]) {
    
    
      System.out.println(message
      + ": [length: " + array.length + "]");
      for (int i = 0; i < array.length; i++) {
    
    
         if (i != 0){
    
    
            System.out.print(", ");
         }
         System.out.print(array[i]);         
      }
      System.out.println();
   }
   private static int[] insertElement(int original[],
   int element, int index) {
    
    
      int length = original.length;
      int destination[] = new int[length + 1];
      System.arraycopy(original, 0, destination, 0, index);
      destination[index] = element;
      System.arraycopy(original, index, destination, index
      + 1, length - index);
      return destination;
   }
}

3.Java 实例 – 获取数组长度

public class Main {
    
    
   public static void main(String args[]) {
    
    
      String[][] data = new String[2][5];
      System.out.println("第一维数组长度: " + data.length);
      System.out.println("第二维数组长度: " + data[0].length);
   }
}

4.Java 实例 – 数组反转

public class RunoobTest {
    
     
  
    /* 反转数组*/
    static void reverse(int a[], int n) 
    {
    
     
        int[] b = new int[n]; 
        int j = n; 
        for (int i = 0; i < n; i++) {
    
     
            b[j - 1] = a[i]; 
            j = j - 1; 
        } 
  
        /*输入反转数组*/
        System.out.println("反转后数组是: \n"); 
        for (int k = 0; k < n; k++) {
    
     
            System.out.println(b[k]); 
        } 
    } 
  
    public static void main(String[] args) 
    {
    
     
        int [] arr = {
    
    10, 20, 30, 40, 50}; 
        reverse(arr, arr.length); 
    } 
}

5.Java 实例 – 数组输出

public class Welcome {
    
    
    public static void main(String[] args){
    
    
        String[] runoobs = new String[3];
        runoobs[0] = "菜鸟教程";
        runoobs[1] = "菜鸟工具";
        runoobs[2] = "菜鸟笔记";
        for (int i = 0; i < runoobs.length; i++){
    
    
            System.out.println(runoobs[i]);
        }
    }
}

6.Java 实例 – 数组获取最大和最小值

import java.util.Arrays;
import java.util.Collections;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        Integer[] numbers = {
    
     8, 2, 7, 1, 4, 9, 5};
        int min = (int) Collections.min(Arrays.asList(numbers));
        int max = (int) Collections.max(Arrays.asList(numbers));
        System.out.println("最小值: " + min);
        System.out.println("最大值: " + max);
    }
}

7.Java 实例 – 数组合并

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
 
public class Main {
    
    
    public static void main(String args[]) {
    
    
        String a[] = {
    
     "A", "E", "I" };
        String b[] = {
    
     "O", "U" };
        List list = new ArrayList(Arrays.asList(a));
        list.addAll(Arrays.asList(b));
        Object[] c = list.toArray();
        System.out.println(Arrays.toString(c));
    }
}

8.Java 实例 – 数组填充

import java.util.*;
 
public class FillTest {
    
    
    public static void main(String args[]) {
    
    
        int array[] = new int[6];
        Arrays.fill(array, 100);
        for (int i=0, n=array.length; i < n; i++) {
    
    
            System.out.println(array[i]);
        }
        System.out.println();
        Arrays.fill(array, 3, 6, 50);
        for (int i=0, n=array.length; i< n; i++) {
    
    
            System.out.println(array[i]);
        }
    }
}

9.Java 实例 – 数组扩容

public class Main {
    
    
    public static void main(String[] args) {
    
    
        String[] names = new String[] {
    
     "A", "B", "C" };
        String[] extended = new String[5];
        extended[3] = "D";
        extended[4] = "E";
        System.arraycopy(names, 0, extended, 0, names.length);
        for (String str : extended){
    
    
            System.out.println(str);
        }
    }
}

10.Java 实例 – 查找数组中的重复元素

public class MainClass {
    
    
    public static void main(String[] args) 
    {
    
    
        int[] my_array = {
    
    1, 2, 5, 5, 6, 6, 7, 2, 9, 2};
        findDupicateInArray(my_array);
 
    }
 
    public static void findDupicateInArray(int[] a) {
    
    
        int count=0;
        for(int j=0;j<a.length;j++) {
    
    
            for(int k =j+1;k<a.length;k++) {
    
    
                if(a[j]==a[k]) {
    
    
                    count++;
                }
            }
            if(count==1)
               System.out.println( "重复元素 : " +  a[j] );
            count = 0;
        }
    }
}

11.Java 实例 – 删除数组元素

import java.util.Arrays;
 
public class RunoobTest {
    
    
 
    public static void main(String[] args) {
    
    
        int[] oldarray = new int[] {
    
    3, 4, 5, 6, 7};// 原始数组
        int num = 2;   // 删除索引为 2 的元素，即删除第三个元素 5
        int[] newArray = new int[oldarray.length-1];// 新数组，长度为原始数组减去 1
        
        for(int i=0;i<newArray.length; i++) {
    
    
            // 判断元素是否越界
            if (num < 0 || num >= oldarray.length) {
    
    
                throw new RuntimeException("元素越界... "); 
            } 
            // 
            if(i<num) {
    
    
                newArray[i] = oldarray[i];
            }
            else {
    
    
                newArray[i] = oldarray[i+1];
            }
        }
        // 打印输出数组内容
        System.out.println(Arrays.toString(oldarray));
        oldarray = newArray;
        System.out.println(Arrays.toString(oldarray));
    }
}

12.Java 实例 – 数组差集

import java.util.ArrayList;
 
public class Main {
    
    
    public static void main(String[] args)  {
    
    
        ArrayList objArray = new ArrayList();
        ArrayList objArray2 = new ArrayList();
        objArray2.add(0,"common1");
        objArray2.add(1,"common2");
        objArray2.add(2,"notcommon");
        objArray2.add(3,"notcommon1");
        objArray.add(0,"common1");
        objArray.add(1,"common2");
        objArray.add(2,"notcommon2");
        System.out.println("array1 的元素" +objArray);
        System.out.println("array2 的元素" +objArray2);
        objArray.removeAll(objArray2);
        System.out.println("array1 与 array2 数组差集为："+objArray);
    }
}

13.Java 实例 – 数组交集

import java.util.ArrayList;
 
public class Main {
    
    
    public static void main(String[] args)  {
    
    
        ArrayList objArray = new ArrayList();
        ArrayList objArray2 = new ArrayList();
        objArray2.add(0,"common1");
        objArray2.add(1,"common2");
        objArray2.add(2,"notcommon");
        objArray2.add(3,"notcommon1");
        objArray.add(0,"common1");
        objArray.add(1,"common2");
        objArray.add(2,"notcommon2");
        System.out.println("array1 数组元素："+objArray);
        System.out.println("array2 数组元素："+objArray2);
        objArray.retainAll(objArray2);
        System.out.println("array2 & array1 数组交集为："+objArray);
    }
}

14.Java 实例 – 在数组中查找指定元素

import java.util.ArrayList;
 
public class Main {
    
    
    public static void main(String[] args)  {
    
    
        ArrayList<String> objArray = new ArrayList<String>();
        ArrayList<String> objArray2 = new ArrayList<String>();
        objArray2.add(0,"common1");
        objArray2.add(1,"common2");
        objArray2.add(2,"notcommon");
        objArray2.add(3,"notcommon1");
        objArray.add(0,"common1");
        objArray.add(1,"common2");
        System.out.println("objArray 的数组元素："+objArray);
        System.out.println("objArray2 的数组元素："+objArray2);
        System.out.println("objArray 是否包含字符串common2? ： "
        +objArray.contains("common2"));
        System.out.println("objArray2 是否包含数组 objArray? ："
        +objArray2.contains(objArray) );
    }
}

15.Java 实例 – 判断数组是否相等

import java.util.Arrays;
 
public class Main {
    
    
    public static void main(String[] args) throws Exception {
    
    
        int[] ary = {
    
    1,2,3,4,5,6};
        int[] ary1 = {
    
    1,2,3,4,5,6};
        int[] ary2 = {
    
    1,2,3,4};
        System.out.println("数组 ary 是否与数组 ary1相等? ："
        +Arrays.equals(ary, ary1));
        System.out.println("数组 ary 是否与数组 ary2相等? ："
        +Arrays.equals(ary, ary2));
    }
}

16.Java 实例 - 数组并集

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
 
 
public class Main {
    
    
    public static void main(String[] args) throws Exception {
    
    
        String[] arr1 = {
    
     "1", "2", "3" };
        String[] arr2 = {
    
     "4", "5", "6" };
        String[] result_union = union(arr1, arr2);
        System.out.println("并集的结果如下：");
 
        for (String str : result_union) {
    
    
            System.out.println(str);
        }
    }
 
    // 求两个字符串数组的并集，利用set的元素唯一性
    public static String[] union(String[] arr1, String[] arr2) {
    
    
        Set<String> set = new HashSet<String>();
 
        for (String str : arr1) {
    
    
            set.add(str);
        }
 
        for (String str : arr2) {
    
    
            set.add(str);
        }
 
        String[] result = {
    
      };
 
        return set.toArray(result);
    }
}

三.Java 时间处理

1.Java 实例 - 格式化时间（SimpleDateFormat）

import java.text.SimpleDateFormat;
import java.util.Date;
 
public class Main{
    
    
    public static void main(String[] args){
    
    
        Date date = new Date();
        String strDateFormat = "yyyy-MM-dd HH:mm:ss";
        SimpleDateFormat sdf = new SimpleDateFormat(strDateFormat);
        System.out.println(sdf.format(date));
    }
}

2.Java 实例 - 获取当前时间

import java.text.SimpleDateFormat;
import java.util.Date;
 
public class Main{
    
    
    public static void main(String[] args){
    
    
        
        SimpleDateFormat sdf = new SimpleDateFormat();// 格式化时间 
        sdf.applyPattern("yyyy-MM-dd HH:mm:ss a");// a为am/pm的标记  
        Date date = new Date();// 获取当前时间 
        System.out.println("现在时间：" + sdf.format(date)); // 输出已经格式化的现在时间（24小时制） 
    } 
}

3.Java 实例 - 获取年份、月份等

import java.util.Calendar;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        Calendar cal = Calendar.getInstance();
        int day = cal.get(Calendar.DATE);
        int month = cal.get(Calendar.MONTH) + 1;
        int year = cal.get(Calendar.YEAR);
        int dow = cal.get(Calendar.DAY_OF_WEEK);
        int dom = cal.get(Calendar.DAY_OF_MONTH);
        int doy = cal.get(Calendar.DAY_OF_YEAR);
 
        System.out.println("当期时间: " + cal.getTime());
        System.out.println("日期: " + day);
        System.out.println("月份: " + month);
        System.out.println("年份: " + year);
        System.out.println("一周的第几天: " + dow);  // 星期日为一周的第一天输出为 1，星期一输出为 2，以此类推
        System.out.println("一月中的第几天: " + dom);
        System.out.println("一年的第几天: " + doy);
    }
}

4.Java 实例 - 时间戳转换成时间

import java.text.SimpleDateFormat;
import java.util.Date;
 
public class Main{
    
    
    public static void main(String[] args){
    
    
        Long timeStamp = System.currentTimeMillis();  //获取当前时间戳
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String sd = sdf.format(new Date(Long.parseLong(String.valueOf(timeStamp))));      // 时间戳转换成时间
        System.out.println("格式化结果：" + sd);
 
        SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy 年 MM 月 dd 日 HH 时 mm 分 ss 秒");
        String sd2 = sdf2.format(new Date(Long.parseLong(String.valueOf(timeStamp))));
        System.out.println("格式化结果：" + sd2);
   }
}

四.Java 方法

1.Java 实例 – 方法重载

class MyClass {
    
    
    int height;
    MyClass() {
    
    
        System.out.println("无参数构造函数");
        height = 4;
    }
    MyClass(int i) {
    
    
        System.out.println("房子高度为 " + i + " 米");
        height = i;
    }
    void info() {
    
    
        System.out.println("房子高度为 " + height + " 米");
    }
    void info(String s) {
    
    
        System.out.println(s + ": 房子高度为 " + height + " 米");
    }
}
public class MainClass {
    
    
    public static void main(String[] args) {
    
    
        MyClass t = new MyClass(3);
        t.info();
        t.info("重载方法");
        //重载构造函数
        new MyClass();
    }
}

2.Java 实例 – 输出数组元素

public class MainClass {
    
    
    public static void printArray(Integer[] inputArray) {
    
    
        for (Integer element : inputArray){
    
    
            System.out.printf("%s ", element);
            System.out.println();
        }
    }
    public static void printArray(Double[] inputArray) {
    
    
        for (Double element : inputArray){
    
    
            System.out.printf("%s ", element);
            System.out.println();
        }
    }
    public static void printArray(Character[] inputArray) {
    
    
        for (Character element : inputArray){
    
    
            System.out.printf("%s ", element);
            System.out.println();
        }
    }
    public static void main(String args[]) {
    
    
        Integer[] integerArray = {
    
     1, 2, 3, 4, 5, 6 };
        Double[] doubleArray = {
    
     1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7 };
        Character[] characterArray = {
    
     'H', 'E', 'L', 'L', 'O' };
        System.out.println("输出整型数组:");
        printArray(integerArray);
        System.out.println("\n输出双精度型数组:");
        printArray(doubleArray);
        System.out.println("\n输出字符型数组:");
        printArray(characterArray);
    }
}

3.Java 实例 – 汉诺塔算法

public class MainClass {
    
    
    public static void main(String[] args) {
    
    
        int nDisks = 3;
        doTowers(nDisks, 'A', 'B', 'C');
    }
    public static void doTowers(int topN, char from, char inter, char to) {
    
    
        if (topN == 1){
    
    
            System.out.println("Disk 1 from "
            + from + " to " + to);
        }else {
    
    
            doTowers(topN - 1, from, to, inter);
            System.out.println("Disk "
            + topN + " from " + from + " to " + to);
            doTowers(topN - 1, inter, from, to);
        }
    }
}

4.Java 实例 – 斐波那契数列

public class MainClass {
    
    
    public static void main(String[] args) {
    
    
        for (int counter = 0; counter <= 10; counter++){
    
    
            System.out.printf("Fibonacci of %d is: %d\n", counter, fibonacci(counter));
        }
    }
 
    public static long fibonacci(long number) {
    
    
        if ((number == 0) || (number == 1))
            return number;
        else
            return fibonacci(number - 1) + fibonacci(number - 2);
    }
}

5.Java 实例 – 阶乘

public class MainClass {
    
    
    public static void main(String args[]) {
    
    
    for (int counter = 0; counter <= 10; counter++){
    
    
        System.out.printf("%d! = %d\n", counter,
        factorial(counter));
    }
    }
    public static long factorial(long number) {
    
    
        if (number <= 1)
            return 1;
        else
            return number * factorial(number - 1);
    }
}

6.Java 实例 – 方法覆盖

public class Findareas{
    
    
    public static void main (String []agrs){
    
    
        Figure f= new Figure(10 , 10);
        Rectangle r= new Rectangle(9 , 5);
        Figure figref;
        figref=f;
        System.out.println("Area is :"+figref.area());
        figref=r;
        System.out.println("Area is :"+figref.area());
    }
}
class Figure{
    
    
    double dim1;
    double dim2;
    Figure(double a , double b) {
    
    
        dim1=a;
        dim2=b;
    }
    Double area() {
    
    
        System.out.println("Inside area for figure.");
        return(dim1*dim2);
    }
}
class Rectangle extends Figure {
    
    
    Rectangle(double a, double b) {
    
    
        super(a ,b);
    }
    Double area() {
    
    
        System.out.println("Inside area for rectangle.");
        return(dim1*dim2);
    }
}

7.Java 实例 – instanceOf 关键字用法

/*
 author by runoob.com
 Main.java
 */
import java.util.ArrayList;
import java.util.Vector;
 
public class Main {
    
    
 
public static void main(String[] args) {
    
    
   Object testObject = new ArrayList();
      displayObjectClass(testObject);
   }
   public static void displayObjectClass(Object o) {
    
    
      if (o instanceof Vector)
      System.out.println("对象是 java.util.Vector 类的实例");
      else if (o instanceof ArrayList)
      System.out.println("对象是 java.util.ArrayList 类的实例");
      else
      System.out.println("对象是 " + o.getClass() + " 类的实例");
   }
}

8.Java 实例 – break 关键字用法

public class Main {
    
    
    public static void main(String[] args) {
    
    
        int[] intary = {
    
     99,12,22,34,45,67,5678,8990 };
        int no = 5678;
        int i = 0;
        boolean found = false;
        for ( ; i < intary.length; i++) {
    
    
            if (intary[i] == no) {
    
    
                found = true;
                break;
            }
        }
        if (found) {
    
    
            System.out.println(no + " 元素的索引位置在: " + i);
        } 
        else {
    
    
            System.out.println(no + " 元素不在数组中");
        }
    }
}

9.Java 实例 – continue 关键字用法

public class Main {
    
    
    public static void main(String[] args) {
    
    
        StringBuffer searchstr = new StringBuffer("hello how are you. ");
        int length = searchstr.length();
        int count = 0;
        for (int i = 0; i < length; i++) {
    
    
            if (searchstr.charAt(i) != 'h')
            continue;
            count++;
            searchstr.setCharAt(i, 'h');
        }
        System.out.println("发现 " + count 
        + " 个 h 字符");
        System.out.println(searchstr);
    }
}

10.Java 实例 – 标签(Label)

public class Main {
    
    
    public static void main(String[] args) {
    
    
        outerLoop:
        for (int i = 0; i < 3; i++) {
    
    
            innerLoop:
            for (int j = 0; j < 3; j++) {
    
    
                if (i == 1 && j == 1) {
    
    
                    break outerLoop; // 跳出外部循环
                }
                System.out.println("i: " + i + ", j: " + j);
            }
        }
    }
}

11.Java 实例 – enum 和 switch 语句使用

enum Car {
    
    
    lamborghini,tata,audi,fiat,honda
}
public class Main {
    
    
    public static void main(String args[]){
    
    
        Car c;
        c = Car.tata;
        switch(c) {
    
    
            case lamborghini:
                System.out.println("你选择了 lamborghini!");
                break;
            case tata:
                System.out.println("你选择了 tata!");
                break;
            case audi:
                System.out.println("你选择了 audi!");
                break;
            case fiat:
                System.out.println("你选择了 fiat!");
                break;
            case honda:
                System.out.println("你选择了 honda!");
                break;
            default:
                System.out.println("我不知道你的车型。");
                break;
        }
    }
}

12.Java 实例 – Enum（枚举）构造函数及方法的使用

enum Car {
    
    
    lamborghini(900),tata(2),audi(50),fiat(15),honda(12);
    private int price;
    Car(int p) {
    
    
        price = p;
    }
    int getPrice() {
    
    
        return price;
    } 
}
public class Main {
    
    
    public static void main(String args[]){
    
    
        System.out.println("所有汽车的价格：");
        for (Car c : Car.values())
        System.out.println(c + " 需要 " 
        + c.getPrice() + " 千美元。");
    }
}

13.Java 实例 – for 和 foreach循环使用

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
 
public class Main
{
    
    
    public static void main(String[] args)
    {
    
    
        int[] arr = {
    
    1, 2, 3, 4, 5};
        
        System.out.println("----------使用 for 循环------------");
        for(int i=0; i<arr.length; i++)
        {
    
    
            System.out.println(arr[i]);
        }
        
        System.out.println("---------使用 For-Each 循环-------------");
        
        //增强的 for 循环 For-Each
        for(int element:arr)
        {
    
    
            System.out.println(element);
        }
        
        System.out.println("---------For-Each 循环二维数组-------------");
        
        //遍历二维数组
        int[][] arr2 = {
    
    {
    
    1, 2, 3}, {
    
    4, 5, 6}, {
    
    7, 8, 9}} ;
        for(int[] row : arr2)
        {
    
    
            for(int element : row)
            {
    
    
                System.out.println(element);
            }
        }
        
        //以三种方式遍历集合 List
        List<String> list = new ArrayList<String>();
        
        list.add("Google");
        list.add("Runoob");
        list.add("Taobao");
        
        System.out.println("----------方式1：普通for循环-----------");
        for(int i = 0; i < list.size(); i++)
        {
    
    
            System.out.println(list.get(i));
        }
        
        System.out.println("----------方式2：使用迭代器-----------");
        for(Iterator<String> iter = list.iterator(); iter.hasNext();)
        {
    
    
            System.out.println(iter.next());
        }
        
        System.out.println("----------方式3：For-Each 循环-----------");
        for(String str: list)
        {
    
    
            System.out.println(str);
        }
    }
}

14.Java 实例 – Varargs 可变参数使用

public class Main {
    
    
    static int  sumvarargs(int... intArrays){
    
    
        int sum, i;
        sum=0;
        for(i=0; i< intArrays.length; i++) {
    
    
            sum += intArrays[i];
        }
        return(sum);
    }
    public static void main(String args[]){
    
    
        int sum=0;
        sum = sumvarargs(new int[]{
    
    10,12,33});
        System.out.println("数字相加之和为: " + sum);
    }
}

15.Java 实例 – 重载(overloading)方法中使用 Varargs

public class Main {
    
    
    static void vaTest(int ... no) {
    
    
        System.out.print("vaTest(int ...): " 
        + "参数个数: " + no.length +" 内容: ");
        for(int n : no)
        System.out.print(n + " ");
        System.out.println();
    }
    static void vaTest(boolean ... bl) {
    
    
        System.out.print("vaTest(boolean ...) " +
        "参数个数: " + bl.length + " 内容: ");
        for(boolean b : bl)
        System.out.print(b + " ");
        System.out.println();
    }
    static void vaTest(String msg, int ... no) {
    
    
        System.out.print("vaTest(String, int ...): " +
        msg +"参数个数: "+ no.length +" 内容: ");
        for(int  n : no)
        System.out.print(n + " ");
        System.out.println();
    }
    public static void main(String args[]){
    
    
        vaTest(1, 2, 3);
        vaTest("测试: ", 10, 20);
        vaTest(true, false, false);
    }
}

五.打印图形

1.Java 实例 – 打印菱形

public class Diamond {
    
    
    public static void main(String[] args) {
    
    
        print(8); // 输出 8 行的菱形
    }
 
    public static void print(int size) {
    
    
        if (size % 2 == 0) {
    
    
            size++; // 计算菱形大小
        }
        for (int i = 0; i < size / 2 + 1; i++) {
    
    
            for (int j = size / 2 + 1; j > i + 1; j--) {
    
    
                System.out.print(" "); // 输出左上角位置的空白
            }
            for (int j = 0; j < 2 * i + 1; j++) {
    
    
                System.out.print("*"); // 输出菱形上半部边缘
            }
            System.out.println(); // 换行
        }
        for (int i = size / 2 + 1; i < size; i++) {
    
    
            for (int j = 0; j < i - size / 2; j++) {
    
    
                System.out.print(" "); // 输出菱形左下角空白
            }
            for (int j = 0; j < 2 * size - 1 - 2 * i; j++) {
    
    
                System.out.print("*"); // 输出菱形下半部边缘
            }
            System.out.println(); // 换行
        }
    }
}

2.Java 实例 – 九九乘法表

public class MultiplicationTable {
    
    
    public static void main(String[] args) {
    
    
        for(int i=1;i<=9;i++) {
    
    
            for(int j=1;j<=i;j++) {
    
    
                System.out.print(j+"×"+i+"="+i*j+"\t");// \t 跳到下一个TAB位置
            }
            System.out.println();
        }
    }
}

3.Java 实例 – 打印三角形

class Demo{
    
    
    public static void main(String[] args){
    
    
        for(int i=1;i<=5;i++){
    
    
            for(int j=5; i<=j; j--)
                System.out.print(" ");
            for(int j=1; j<=i; j++)
                System.out.print("*");
            for(int j=1; j<i; j++)
                System.out.print("*");
            System.out.println();
        }
    }
}

4.Java 实例 – 打印倒立的三角形

public class InvertedTriangle {
    
    
    public static void main(String[] args) {
    
    
         //打印倒立的三角形
        for (int m = 1; m <= 4; m++) {
    
    
            //打印空格
            for (int n = 0; n <= m; n++) {
    
    
                System.out.print(" ");
            }
            //打印*
            for (int x = 1; x <= 7 -2 * (m - 1); x++) {
    
    
                System.out.print("*");
            }
            System.out.println();
        }        
    }
}

5.Java 实例 – 打印平行四边形

public class Parallelogram {
    
    
    public static void main(String[] args) {
    
    
         //外层循环 每次打出一个*
        for (int i = 1; i <=5; i++) {
    
    
            //填充空格
            for (int j = 1; j <= 5 - i; j++) {
    
    
                System.out.print(" ");
            }
            //内层循环 每次打印一个*
            for (int k = 1; k <= 5; k++) {
    
    
                System.out.print("*");
            }
            System.out.println();
        }
    }
}

6.Java 实例 – 打印矩形

public class Rect {
    
    
    public static void main(String[] args) {
    
    
         //外层循环 每次输出一行*
        for (int i = 1; i <= 5; i++) {
    
    
            System.out.print("*");
            //内层循环 每次输出一个*
            for (int j = 1; j <= 5; j++) {
    
    
                System.out.print("*");
            }
            System.out.println();
        }
    }
}

六.Java 文件操作

1.Java 实例 - 文件写入

/*
 author by runoob.com 
 Main.java
 */
 
import java.io.*;
 
public class Main {
    
    
    public static void main(String[] args)  {
    
    
        try {
    
    
            BufferedWriter out = new BufferedWriter(new FileWriter("runoob.txt"));
            out.write("菜鸟教程");
            out.close();
            System.out.println("文件创建成功！");
        } catch (IOException e) {
    
    
        }
    }
}

2.Java 实例 - 读取文件内容

import java.io.*;
 
public class Main {
    
    
    public static void main(String[] args)  {
    
    
        try {
    
    
            BufferedReader in = new BufferedReader(new FileReader("test.log"));
            String str;
            while ((str = in.readLine()) != null) {
    
    
                System.out.println(str);
            }
            System.out.println(str);
        } catch (IOException e) {
    
    
        }
    }
}

3.Java 实例 - 删除文件

import java.io.*;
 
public class Main
{
    
    
    public static void main(String[] args)
    {
    
    
        try{
    
    
            File file = new File("c:\\test.txt");
            if(file.delete()){
    
    
                System.out.println(file.getName() + " 文件已被删除！");
            }else{
    
    
                System.out.println("文件删除失败！");
            }
        }catch(Exception e){
    
    
            e.printStackTrace();
        }
    }
}

4.Java 实例 - 将文件内容复制到另一个文件

import java.io.*;
 
public class Main {
    
    
    public static void main(String[] args) throws Exception {
    
    
        BufferedWriter out1 = new BufferedWriter(new FileWriter("srcfile"));
        out1.write("string to be copied\n");
        out1.close();
        InputStream in = new FileInputStream(new File("srcfile"));
        OutputStream out = new FileOutputStream
        (new File("destnfile"));
        byte[] buf = new byte[1024];
        int len;
        while ((len = in.read(buf)) > 0) {
    
    
            out.write(buf, 0, len);
        }
        in.close();
        out.close();
        BufferedReader in1 = new BufferedReader(new FileReader("destnfile"));
        String str;
        while ((str = in1.readLine()) != null) {
    
    
            System.out.println(str);
        }
        in1.close();
    }
}

5.Java 实例 - 向文件中追加数据

import java.io.*;
 
public class Main {
    
    
    public static void main(String[] args) throws Exception {
    
    
        try {
    
    
            BufferedWriter out = new BufferedWriter(new FileWriter("filename"));
            out.write("aString1\n");
            out.close();
            out = new BufferedWriter(new FileWriter("filename",true));
            out.write("aString2");
            out.close();
            BufferedReader in = new BufferedReader(new FileReader("filename"));
            String str;
            while ((str = in.readLine()) != null) {
    
    
                System.out.println(str);
            }
            in.close();
        }
            catch (IOException e) {
    
    
            System.out.println("exception occoured"+ e);
        }
    }
}

6.Java 实例 - 创建临时文件

import java.io.*;
 
public class Main {
    
    
    public static void main(String[] args) throws Exception {
    
    
        File temp = File.createTempFile("testrunoobtmp", ".txt");
        System.out.println("文件路径: "+temp.getAbsolutePath());
        temp.deleteOnExit();
        BufferedWriter out = new BufferedWriter(new FileWriter(temp));
        out.write("aString");
        System.out.println("临时文件已创建:");
        out.close();
    }
}

7.Java 实例 - 修改文件最后的修改日期

import java.io.File;
import java.util.Date;
 
public class Main {
    
    
    public static void main(String[] args) throws Exception {
    
    
        File fileToChange = new File("C:/myjavafile.txt");
        fileToChange.createNewFile();
        Date filetime = new Date(fileToChange.lastModified());
        System.out.println(filetime.toString());
        System.out.println(fileToChange.setLastModified(System.currentTimeMillis()));
        filetime = new Date(fileToChange.lastModified());
        System.out.println(filetime.toString());
    }
}

8.Java 实例 - 获取文件大小

import java.io.File;
 
public class Main {
    
    
    public static long getFileSize(String filename) {
    
    
        File file = new File(filename);
        if (!file.exists() || !file.isFile()) {
    
    
            System.out.println("文件不存在");
            return -1;
        }
        return file.length();
    }
    public static void main(String[] args) {
    
    
        long size = getFileSize("c:/java.txt");
        System.out.println("java.txt文件大小为: " + size);
    }
}

9.Java 实例 - 文件重命名

import java.io.File;
import java.io.IOException;
 
public class RunoobTest {
    
    
    public static void main(String[] args) throws IOException {
    
    
        // 旧的文件或目录
        File oldName = new File("./runoob-test.txt");
        // 新的文件或目录
        File newName = new File("./runoob-test-2.txt");
        if (newName.exists()) {
    
      //  确保新的文件名不存在
            throw new java.io.IOException("file exists");
        }
        if(oldName.renameTo(newName)) {
    
    
            System.out.println("已重命名");
        } else {
    
    
            System.out.println("Error");
        }
    }
}

10.Java 实例 - 设置文件只读

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        File file = new File("C:/java.txt");
        System.out.println(file.setReadOnly());
        System.out.println(file.canWrite());
    }
}

11.Java 实例 - 检测文件是否存在

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        File file = new File("C:/java.txt");
        System.out.println(file.exists());
    }
}

12.Java 实例 - 在指定目录中创建文件

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] args) throws Exception {
    
    
        File file = null;
        File dir = new File("C:/");
        file = File.createTempFile
        ("JavaTemp", ".javatemp", dir);
        System.out.println(file.getPath());
    }
}

13.Java 实例 - 获取文件修改时间

import java.io.File;
import java.util.Date;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        File file = new File("Main.java");
        Long lastModified = file.lastModified();
        Date date = new Date(lastModified);
        System.out.println(date);
    }
}

14.Java 实例 - 创建文件

import java.io.File;
import java.io.IOException;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        try{
    
    
            File file = new File("C:/myfile.txt");
            if(file.createNewFile())
                System.out.println("文件创建成功！");
            else
                System.out.println("出错了，该文件已经存在。");
        }
        catch(IOException ioe) {
    
    
            ioe.printStackTrace();
        }
    }
}

15.Java 实例 - 文件路径比较

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        File file1 = new File("C:/File/demo1.txt");
        File file2 = new File("C:/java/demo1.txt");
        if(file1.compareTo(file2) == 0) {
    
    
            System.out.println("文件路径一致！");
        } else {
    
    
            System.out.println("文件路径不一致！");
        }
    }
}

七.Java 目录操作

1.Java 实例 - 递归创建目录

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        String directories = "D:\\a\\b\\c\\d\\e\\f\\g\\h\\i";
        File file = new File(directories);
        boolean result = file.mkdirs();
        System.out.println("Status = " + result);
    }
}

2.Java 实例 - 删除目录

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] argv) throws Exception {
    
    
        // 删除当前目录下的 test 目录
        deleteDir(new File("./test"));
    }
    public static boolean deleteDir(File dir) {
    
    
        if (dir.isDirectory()) {
    
    
            String[] children = dir.list();
            for (int i = 0; i < children.length; i++) {
    
    
                boolean success = deleteDir
                (new File(dir, children[i]));
                if (!success) {
    
    
                    return false;
                }
            }
        }
        if(dir.delete()) {
    
    
            System.out.println("目录已被删除！");
            return true;
        } else {
    
    
            System.out.println("目录删除失败！");
            return false;
        }
    }
}

3.Java 实例 - 判断目录是否为空

import java.io.File;
 
public class Main
{
    
    
    public static void main(String[] args)
    {
    
    
        File file = new File("./testdir");  // 当前目录下的 testdir目录
        if(file.isDirectory()){
    
    
            if(file.list().length>0){
    
    
                System.out.println("目录不为空!");
            }else{
    
    
                System.out.println("目录为空!");
            }
        }else{
    
    
            System.out.println("这不是一个目录!");
        }
    }
}

4.Java 实例 - 判断文件是否隐藏

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        File file = new File("C:/Demo.txt");
        System.out.println(file.isHidden());
    }
}

5.Java 实例 - 获取目录大小

import java.io.File;
import org.apache.commons.io.FileUtils;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        long size = FileUtils.sizeOfDirectory(new File("C:/test"));
        System.out.println("Size: " + size + " bytes");
    }
}

6.Java 实例 - 在指定目录中查找文件

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] argv) throws Exception {
    
    
        File dir = new File("../java");
        String[] children = dir.list();
        if (children == null) {
    
    
            System.out.println("该目录不存在");
        }
        else {
    
    
            for (int i = 0; i < children.length; i++) {
    
    
                String filename = children[i];
                System.out.println(filename);
            }
        }
    }
}

7.Java 实例 - 获取文件的上级目录

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        File file = new File("C:/File/demo.txt");
        String strParentDirectory = file.getParent();
        System.out.println("文件的上级目录为 : " + strParentDirectory);
    }
}

8.Java 实例 - 获取目录最后修改时间

import java.io.File;
import java.util.Date;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        File file = new File("C://FileIO//demo.txt");
        System.out.println("最后修改时间：" + new Date(file.lastModified()));
    }
}

9.Java 实例 - 打印目录结构

import java.io.File;
import java.io.IOException;
 
public class FileUtil {
    
    
    public static void main(String[] a)throws IOException{
    
    
        showDir(1, new File("d:\\Java"));
    }
    static void showDir(int indent, File file) throws IOException {
    
    
        for (int i = 0; i < indent; i++)
            System.out.print('-');
        System.out.println(file.getName());
        if (file.isDirectory()) {
    
    
            File[] files = file.listFiles();
            for (int i = 0; i < files.length; i++)
                showDir(indent + 4, files[i]);
        }
    }
}

10.Java 实例 - 遍历指定目录下的所有目录

import java.io.*;
 
class Main {
    
    
   public static void main(String[] args) {
    
    
      File dir = new File("F:");
      File[] files = dir.listFiles();
      FileFilter fileFilter = new FileFilter() {
    
    
         public boolean accept(File file) {
    
    
            return file.isDirectory();
         }
      };
      files = dir.listFiles(fileFilter);
      System.out.println(files.length);
      if (files.length == 0) {
    
    
         System.out.println("目录不存在或它不是一个目录");
      }
      else {
    
    
         for (int i=0; i< files.length; i++) {
    
    
            File filename = files[i];
            System.out.println(filename.toString());
         }
      }
   }
}

11.Java 实例 - 遍历指定目录下的所有文件

import java.io.File;
 
class Main {
    
    
    public static void main(String[] args) {
    
    
        File dir = new File("C:");
        String[] children = dir.list();
        if (children == null) {
    
    
            System.out.println( "目录不存在或它不是一个目录");
        }
        else {
    
    
            for (int i=0; i< children.length; i++) {
    
    
                String filename = children[i];
                System.out.println(filename);
            }
        }
    }
}

12.Java 实例 - 在指定目录中查找文件

import java.io.*;
 
class Main {
    
    
   public static void main(String[] args) {
    
    
      File dir = new File("C:");
      FilenameFilter filter = new FilenameFilter() {
    
    
         public boolean accept
         (File dir, String name) {
    
    
            return name.startsWith("b");
        }
      };
      String[] children = dir.list(filter);
      if (children == null) {
    
    
         System.out.println("目录不存在或它不是一个目录");
      } 
      else {
    
    
         for (int i=0; i < children.length; i++) {
    
    
            String filename = children[i];
            System.out.println(filename);
         }
      } 
   }
}

13.Java 实例 - 遍历系统根目录

import java.io.*;
 
class Main{
    
    
    public static void main(String[] args){
    
    
        File[] roots = File.listRoots();
        System.out.println("系统所有根目录：");
        for (int i=0; i < roots.length; i++) {
    
    
            System.out.println(roots[i].toString());
        }
    }
}

14.Java 实例 - 查看当前工作目录

class Main {
    
    
    public static void main(String[] args) {
    
    
        String curDir = System.getProperty("user.dir");
        System.out.println("你当前的工作目录为 :" + curDir);
    }
}

15.Java 实例 - 遍历目录

import java.io.File;
 
public class Main {
    
    
    public static void main(String[] argv) throws Exception {
    
    
        System.out.println("遍历目录");
        File dir = new File("/www/java"); //要遍历的目录
        visitAllDirsAndFiles(dir);
    }
    public static void visitAllDirsAndFiles(File dir) {
    
    
        System.out.println(dir);
        if (dir.isDirectory()) {
    
    
            String[] children = dir.list();
            for (int i = 0; i < children.length; i++) {
    
    
                visitAllDirsAndFiles(new File(dir, children[i]));
            }
        }
    }
}

八.Java 异常处理

1.Java 实例 - 异常处理方法

class ExceptionDemo
{
    
    
    public static void main(String[] args) {
    
    
        try {
    
    
            throw new Exception("My Exception");
        } catch (Exception e) {
    
    
            System.err.println("Caught Exception");
            System.err.println("getMessage():" + e.getMessage());
            System.err.println("getLocalizedMessage():" + e.getLocalizedMessage());
            System.err.println("toString():" + e);
            System.err.println("printStackTrace():");
            e.printStackTrace();
        }
    }
}

2.Java 实例 - 多个异常处理（多个catch）

class Demo  
{
    
      
    int div(int a,int b) throws ArithmeticException,ArrayIndexOutOfBoundsException//在功能上通过throws的关键字声明该功能可能出现问题  
    {
    
      
        int []arr = new int [a];  
  
        System.out.println(arr[4]);//制造的第一处异常  
  
        return a/b;//制造的第二处异常  
    }  
}  
  
  
class ExceptionDemo  
{
    
      
    public static void main(String[]args) //throws Exception  
    {
    
      
        Demo d = new Demo();  
  
        try  
            {
    
      
                int x = d.div(4,0);//程序运行截图中的三组示例 分别对应此处的三行代码  
                //int x = d.div(5,0);  
                //int x = d.div(4,1);  
                System.out.println("x="+x);   
        }  
        catch (ArithmeticException e)  
        {
    
      
            System.out.println(e.toString());  
        }  
        catch (ArrayIndexOutOfBoundsException e)  
        {
    
      
            System.out.println(e.toString());  
        }  
        catch (Exception e)//父类 写在此处是为了捕捉其他没预料到的异常 只能写在子类异常的代码后面  
                            //不过一般情况下是不写的   
        {
    
      
            System.out.println(e.toString());  
        }  
          
  
  
        System.out.println("Over");  
    }  
  
}

3.Java 实例 - Finally的用法

public class ExceptionDemo2 {
    
    
   public static void main(String[] argv) {
    
    
      new ExceptionDemo2().doTheWork();
   }
   public void doTheWork() {
    
    
      Object o = null;
      for (int i=0; i<5; i++) {
    
    
         try {
    
    
            o = makeObj(i);
         }
         catch (IllegalArgumentException e) {
    
    
            System.err.println
            ("Error: ("+ e.getMessage()+").");
            return;   
         }
         finally {
    
    
            System.err.println("都已执行完毕");
            if (o==null)
            System.exit(0);
        }
        System.out.println(o); 
      }
   }
   public Object makeObj(int type) 
   throws IllegalArgumentException {
    
    
      if (type == 1)  
      throw new IllegalArgumentException
      ("不是指定的类型： " + type);
      return new Object();
   }
}

4.Java 实例 - 使用 catch 处理异常

public class Main {
    
    
    public static void main (String args[]) {
    
    
        int array[]={
    
    20,20,40};
        int num1=15,num2=10;
        int result=10;
        try{
    
    
            result = num1/num2;
            System.out.println("结果为 " +result);
            for(int i =5;i >=0; i--) {
    
    
                System.out.println ("数组的元素值为 " +array[i]);
            }
        }
        catch (Exception e) {
    
    
            System.out.println("触发异常 : "+e);
        }
    }
}

5.Java 实例 - 多线程异常处理

class MyThread extends Thread{
    
    
    public void run(){
    
    
        System.out.println("Throwing in " +"MyThread");
        throw new RuntimeException();
    }
}
class Main {
    
    
    public static void main(String[] args){
    
    
        MyThread t = new MyThread();
        t.start();
        try{
    
    
            Thread.sleep(1000);
        }
        catch (Exception x){
    
    
            System.out.println("Caught it" + x);
        }
        System.out.println("Exiting main");
    }
}

6.Java 实例 - 获取异常的堆栈信息

public class Main{
    
    
    public static void main (String args[]){
    
    
        int array[]={
    
    20,20,40};
        int num1=15,num2=10;
        int result=10;
        try{
    
    
            result = num1/num2;
            System.out.println("The result is" +result);
            for(int i =5; i>=0; i--) {
    
    
                System.out.println("The value of array is" +array[i]);
            }
        }
        catch (Exception e) {
    
    
            e.printStackTrace();
        }
    }
}

7.Java 实例 - 重载方法异常处理

public class Main {
    
    
    double method(int i) throws Exception{
    
    
        return i/0;
    }
    boolean method(boolean b) {
    
    
        return !b;
    }
    static double method(int x, double y) throws Exception  {
    
    
        return x + y ;
    }
    static double method(double x, double y) {
    
    
        return x + y - 3;
    }   
    public static void main(String[] args) {
    
    
        Main mn = new Main();
        try{
    
    
            System.out.println(method(10, 20.0));
            System.out.println(method(10.0, 20));
            System.out.println(method(10.0, 20.0));
            System.out.println(mn.method(10));
        }
        catch (Exception ex){
    
    
            System.out.println("exception occoure: "+ ex);
        }
    }
}

8.Java 实例 - 链试异常

public class Main {
    
    
    public static void main (String args[])throws Exception  {
    
    
        int n=20,result=0;
        try{
    
    
            result=n/0;
            System.out.println("结果为"+result);
        }
        catch(ArithmeticException ex){
    
    
            System.out.println("发算术异常: "+ex);
            try {
    
    
                throw new NumberFormatException();
            }
            catch(NumberFormatException ex1) {
    
    
                System.out.println("手动抛出链试异常 : "+ex1);
            }
        }
    }
}

9.Java 实例 - 自定义异常

class WrongInputException extends Exception {
    
      // 自定义的类
    WrongInputException(String s) {
    
    
        super(s);
    }
}
class Input {
    
    
    void method() throws WrongInputException {
    
    
        throw new WrongInputException("Wrong input"); // 抛出自定义的类
    }
}
class TestInput {
    
    
    public static void main(String[] args){
    
    
        try {
    
    
            new Input().method();
        }
        catch(WrongInputException wie) {
    
    
            System.out.println(wie.getMessage());
        }
    } 
}

九.Java 数据结构

1.Java 实例 – 数字求和运算

public class Main {
    
    
    public static void main(String[] args) {
    
    
        int limit=100;
        int sum=0;
        int i=1;
        do
        {
    
    
            sum=sum+i;
            i++;
        }
        while(i<=limit);
        System.out.println("sum="+sum);
    }
}

2.Java 实例 – 利用堆栈将中缀表达式转换成后缀

import java.io.IOException;
 
public class InToPost {
    
    
   private Stack theStack;
   private String input;
   private String output = "";
   public InToPost(String in) {
    
    
      input = in;
      int stackSize = input.length();
      theStack = new Stack(stackSize);
   }
   public String doTrans() {
    
    
      for (int j = 0; j < input.length(); j++) {
    
    
         char ch = input.charAt(j);
         switch (ch) {
    
    
            case '+': 
            case '-':
            gotOper(ch, 1); 
            break; 
            case '*': 
            case '/':
            gotOper(ch, 2); 
            break; 
            case '(': 
            theStack.push(ch);
            break;
            case ')': 
            gotParen(ch); 
            break;
            default: 
            output = output + ch; 
            break;
         }
      }
      while (!theStack.isEmpty()) {
    
    
         output = output + theStack.pop();
      }
      System.out.println(output);
      return output; 
   }
   public void gotOper(char opThis, int prec1) {
    
    
      while (!theStack.isEmpty()) {
    
    
         char opTop = theStack.pop();
         if (opTop == '(') {
    
    
            theStack.push(opTop);
            break;
         }
         else {
    
    
            int prec2;
            if (opTop == '+' || opTop == '-')
            prec2 = 1;
            else
            prec2 = 2;
            if (prec2 < prec1) {
    
     
               theStack.push(opTop);
               break;
            }
            else
            output = output + opTop;
         }
      }
      theStack.push(opThis);
   }
   public void gotParen(char ch){
    
     
      while (!theStack.isEmpty()) {
    
    
         char chx = theStack.pop();
         if (chx == '(') 
         break; 
         else
         output = output + chx; 
      }
   }
   public static void main(String[] args) 
   throws IOException {
    
    
      String input = "1+2*4/5-7+3/6";
      String output;
      InToPost theTrans = new InToPost(input);
      output = theTrans.doTrans(); 
      System.out.println("Postfix is " + output + '\n');
   }
   class Stack {
    
    
      private int maxSize;
      private char[] stackArray;
      private int top;
      public Stack(int max) {
    
    
         maxSize = max;
         stackArray = new char[maxSize];
         top = -1;
      }
      public void push(char j) {
    
    
         stackArray[++top] = j;
      }
      public char pop() {
    
    
         return stackArray[top--];
      }
      public char peek() {
    
    
         return stackArray[top];
      }
      public boolean isEmpty() {
    
    
         return (top == -1);
     }
   }
}

3.Java 实例 – 在链表（LinkedList）的开头和结尾

import java.util.LinkedList;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        LinkedList<String> lList = new LinkedList<String>();
        lList.add("1");
        lList.add("2");
        lList.add("3");
        lList.add("4");
        lList.add("5");
        System.out.println(lList);
        lList.addFirst("0");
        System.out.println(lList);
        lList.addLast("6");
        System.out.println(lList);
    }
}

4.Java 实例 – 获取链表（LinkedList）的第一个

import java.util.LinkedList;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        LinkedList<String> lList = new LinkedList<String>();
        lList.add("100");
        lList.add("200");
        lList.add("300");
        lList.add("400");
        lList.add("500");
        System.out.println("链表的第一个元素是：" + lList.getFirst());
        System.out.println("链表的最后一个元素是：" + lList.getLast());
    }
}

5.Java 实例 – 删除链表中的元素

import java.util.*;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      LinkedList<String> lList = new LinkedList<String>();
      lList.add("1");
      lList.add("8");
      lList.add("6");
      lList.add("4");
      lList.add("5");
      System.out.println(lList);
      lList.subList(2, 4).clear();
      System.out.println(lList);
   }
}

6.Java 实例 – 获取链表的元素

import java.util.*;
 
public class Main {
    
    
   private LinkedList list = new LinkedList();
   public void push(Object v) {
    
    
      list.addFirst(v);
   }
   public Object top() {
    
    
      return list.getFirst();
   }
   public Object pop() {
    
    
      return list.removeFirst();
   }
   public static void main(String[] args) {
    
    
      Main stack = new Main();
      for (int i = 30; i < 40; i++)
         stack.push(new Integer(i));
      System.out.println(stack.top());
      System.out.println(stack.pop());
      System.out.println(stack.pop());
      System.out.println(stack.pop());
   }
}

7.Java 实例 – 获取向量元素的索引值

import java.util.Collections;
import java.util.Vector;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      Vector v = new Vector();
      v.add("X");
      v.add("M");
      v.add("D");
      v.add("A");
      v.add("O");
      Collections.sort(v);
      System.out.println(v);
      int index = Collections.binarySearch(v, "D");
      System.out.println("元素索引值为 : " + index);
   }
}

8.Java 实例 – 栈的实现

]`public class MyStack {
    
    
   private int maxSize;
   private long[] stackArray;
   private int top;
   public MyStack(int s) {
    
    
      maxSize = s;
      stackArray = new long[maxSize];
      top = -1;
   }
   public void push(long j) {
    
    
      stackArray[++top] = j;
   }
   public long pop() {
    
    
      return stackArray[top--];
   }
   public long peek() {
    
    
      return stackArray[top];
   }
   public boolean isEmpty() {
    
    
      return (top == -1);
   }
   public boolean isFull() {
    
    
      return (top == maxSize - 1);
   }
   public static void main(String[] args) {
    
    
      MyStack theStack = new MyStack(10); 
      theStack.push(10);
      theStack.push(20);
      theStack.push(30);
      theStack.push(40);
      theStack.push(50);
      while (!theStack.isEmpty()) {
    
    
         long value = theStack.pop();
         System.out.print(value);
         System.out.print(" ");
      }
      System.out.println("");
   }
}`

9.Java 实例 – 链表元素查找

import java.util.LinkedList;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      LinkedList lList = new LinkedList();
      lList.add("1");
      lList.add("2");
      lList.add("3");
      lList.add("4");
      lList.add("5");
      lList.add("2");
      System.out.println("元素 2 第一次出现的位置：" + lList.indexOf("2"));
      System.out.println("元素 2 最后一次出现的位置："+ lList.lastIndexOf("2"));
   }
}

10.Java 实例 – 压栈出栈的方法实现字符串反转

import java.io.IOException;
 
public class StringReverserThroughStack {
    
    
   private String input; 
   private String output;
   public StringReverserThroughStack(String in) {
    
    
      input = in;
   }
   public String doRev() {
    
    
      int stackSize = input.length(); 
      Stack theStack = new Stack(stackSize); 
      for (int i = 0; i < input.length(); i++) {
    
    
         char ch = input.charAt(i); 
         theStack.push(ch); 
      }
      output = "";
      while (!theStack.isEmpty()) {
    
    
         char ch = theStack.pop(); 
         output = output + ch; 
      }
      return output;
   }
   public static void main(String[] args) 
   throws IOException {
    
    
      String input = "www.w3cschool.cc";
      String output;
      StringReverserThroughStack theReverser = 
      new StringReverserThroughStack(input);
      output = theReverser.doRev();
      System.out.println("反转前： " + input);
      System.out.println("反转后： " + output);
   }
   class Stack {
    
    
      private int maxSize;
      private char[] stackArray;
      private int top;
      public Stack(int max) {
    
    
         maxSize = max;
         stackArray = new char[maxSize];
         top = -1;
      }
      public void push(char j) {
    
    
         stackArray[++top] = j;
      }
      public char pop() {
    
    
         return stackArray[top--];
      }
      public char peek() {
    
    
         return stackArray[top];
      }
      public boolean isEmpty() {
    
    
         return (top == -1);
      }
   }
}

11.Java 实例 – 队列（Queue）用法

import java.util.LinkedList;
import java.util.Queue;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        //add()和remove()方法在失败的时候会抛出异常(不推荐)
        Queue<String> queue = new LinkedList<String>();
        //添加元素
        queue.offer("a");
        queue.offer("b");
        queue.offer("c");
        queue.offer("d");
        queue.offer("e");
        for(String q : queue){
    
    
            System.out.println(q);
        }
        System.out.println("===");
        System.out.println("poll="+queue.poll()); //返回第一个元素，并在队列中删除
        for(String q : queue){
    
    
            System.out.println(q);
        }
        System.out.println("===");
        System.out.println("element="+queue.element()); //返回第一个元素 
        for(String q : queue){
    
    
            System.out.println(q);
        }
        System.out.println("===");
        System.out.println("peek="+queue.peek()); //返回第一个元素 
        for(String q : queue){
    
    
            System.out.println(q);
        }
    }
}

12.Java 实例 – 获取向量的最大元素

import java.util.Collections;
import java.util.Vector;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      Vector v = new Vector();
      v.add(new Double("3.4324"));
      v.add(new Double("3.3532"));
      v.add(new Double("3.342"));
      v.add(new Double("3.349"));
      v.add(new Double("2.3"));
      Object obj = Collections.max(v);
      System.out.println("最大元素是："+obj);
   }
}

13.Java 实例 – 链表修改

import java.util.LinkedList;
 
public class Main {
    
    
   public static void main(String[] a) {
    
    
      LinkedList officers = new LinkedList();
      officers.add("B");
      officers.add("B");
      officers.add("T");
      officers.add("H");
      officers.add("P");
      System.out.println(officers);
      officers.set(2, "M");
      System.out.println(officers);
   }
}

14.Java 实例 – 旋转向量

import java.util.Collections;
import java.util.Vector;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      Vector<String> v = new Vector();
      v.add("1");
      v.add("2");
      v.add("3");
      v.add("4");
      v.add("5");
      System.out.println(v);
      Collections.swap(v, 0, 4);
      System.out.println("旋转后");
      System.out.println(v);
   }
}

十.Java 集合

1.Java 实例 – 数组转集合

import java.util.*;
import java.io.*;
 
public class ArrayToCollection{
    
    
   public static void main(String args[]) 
   throws IOException{
    
    
      int n = 5;         // 5 个元素
      String[] name = new String[n];
      for(int i = 0; i < n; i++){
    
    
         name[i] = String.valueOf(i);
      }
      List<String> list = Arrays.asList(name); 
      System.out.println();
      for(String li: list){
    
    
         String str = li;
         System.out.print(str + " ");
      }
   }
}

2.Java 实例 – 集合比较

import java.util.Collections;
import java.util.Set;
import java.util.TreeSet;
 
class Main {
    
    
    public static void main(String[] args) {
    
    
        String[] coins = {
    
     "Penny", "nickel", "dime", "Quarter", "dollar" };
        Set<String> set = new TreeSet<String>();
        for (int i = 0; i < coins.length; i++) {
    
    
            set.add(coins[i]);
        }
        System.out.println(Collections.min(set));
        System.out.println(Collections.min(set, String.CASE_INSENSITIVE_ORDER));
        for (int i = 0; i <= 10; i++) {
    
    
            System.out.print("-");
        }
        System.out.println("");
        System.out.println(Collections.max(set));
        System.out.println(Collections.max(set, String.CASE_INSENSITIVE_ORDER));
    }
}

3.Java 实例 – HashMap遍历

import java.util.*;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      HashMap< String, String> hMap = 
      new HashMap< String, String>();
      hMap.put("1", "1st");
      hMap.put("2", "2nd");
      hMap.put("3", "3rd");
      Collection cl = hMap.values();
      Iterator itr = cl.iterator();
      while (itr.hasNext()) {
    
    
         System.out.println(itr.next());
     }
   }
}

4.Java 实例 – 集合长度

import java.util.*;
 
public class Main {
    
    
   public static void main(String [] args) {
    
       
      System.out.println( "集合实例!\n" ); 
      int size;
      HashSet collection = new HashSet ();
      String str1 = "Yellow", str2 = "White", str3 = 
      "Green", str4 = "Blue";  
      Iterator iterator;
      collection.add(str1);    
      collection.add(str2);   
      collection.add(str3);   
      collection.add(str4);
      System.out.print("集合数据: ");  
      iterator = collection.iterator();     
      while (iterator.hasNext()){
    
    
         System.out.print(iterator.next() + " ");  
      }
      System.out.println();
      size = collection.size();
      if (collection.isEmpty()){
    
    
         System.out.println("集合是空的");
      }
      else{
    
    
         System.out.println( "集合长度: " + size);
      }
      System.out.println();
   }
}

5.Java 实例 – 集合打乱顺序

import java.util.*;
 
public class Main {
    
    
    public static void main(String[] args) {
    
    
        List<Integer> list = new ArrayList<Integer>();
        for (int i = 0; i < 10; i++)
            list.add(new Integer(i));
        System.out.println("打乱前:");
        System.out.println(list);
 
        for (int i = 1; i < 6; i++) {
    
    
            System.out.println("第" + i + "次打乱：");
            Collections.shuffle(list);
            System.out.println(list);
        }
    }
}

6.Java 实例 – 集合遍历

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
 
public class Main {
    
    
 
   public static void main(String[] args) {
    
    
      // List集合的遍历
      listTest();
      // Set集合的遍历
      setTest();
   }
 
   private static void setTest() {
    
    
      Set<String> set = new HashSet<String>();
      set.add("JAVA");
      set.add("C");
      set.add("C++");
      // 重复数据添加失败
      set.add("JAVA");
      set.add("JAVASCRIPT");
 
      // 使用iterator遍历set集合
      Iterator<String> it = set.iterator();
      while (it.hasNext()) {
    
    
         String value = it.next();
         System.out.println(value);
      }
      
      // 使用增强for循环遍历set集合
      for(String s: set){
    
    
         System.out.println(s);
      }
   }
 
   // 遍历list集合
   private static void listTest() {
    
    
      List<String> list = new ArrayList<String>();
      list.add("菜");
      list.add("鸟");
      list.add("教");
      list.add("程");
      list.add("www.runoob.com");
 
      // 使用iterator遍历
      Iterator<String> it = list.iterator();
      while (it.hasNext()) {
    
    
         String value = it.next();
         System.out.println(value);
      }
 
      // 使用传统for循环进行遍历
      for (int i = 0, size = list.size(); i < size; i++) {
    
    
         String value = list.get(i);
         System.out.println(value);
      }
 
      // 使用增强for循环进行遍历
      for (String value : list) {
    
    
         System.out.println(value);
      }
   }
}

7.Java 实例 – 集合反转

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ListIterator;
 
class Main {
    
    
   public static void main(String[] args) {
    
    
      String[] coins = {
    
     "A", "B", "C", "D", "E" };
      List l = new ArrayList();
      for (int i = 0; i < coins.length; i++)
         l.add(coins[i]);
      ListIterator liter = l.listIterator();
      System.out.println("反转前");
      while (liter.hasNext())
         System.out.println(liter.next());
      Collections.reverse(l);
      liter = l.listIterator();
      System.out.println("反转后");
      while (liter.hasNext())
         System.out.println(liter.next());
   }
}

8.Java 实例 – 删除集合中指定元素

import java.util.*;
 
public class Main {
    
    
   public static void main(String [] args) {
    
       
      System.out.println( "集合实例!\n" ); 
      int size;
      HashSet collection = new HashSet ();
      String str1 = "Yellow", str2 = "White", str3 = 
      "Green", str4 = "Blue";  
      Iterator iterator;
      collection.add(str1);    
      collection.add(str2);   
      collection.add(str3);   
      collection.add(str4);
      System.out.print("集合数据: ");  
      iterator = collection.iterator();     
      while (iterator.hasNext()){
    
    
         System.out.print(iterator.next() + " ");  
      }
      System.out.println();
      collection.remove(str2);
      System.out.println("删除之后 [" + str2 + "]\n");
      System.out.print("现在集合的数据是: ");
      iterator = collection.iterator();     
      while (iterator.hasNext()){
    
    
         System.out.print(iterator.next() + " ");  
      }
      System.out.println();
      size = collection.size();
      System.out.println("集合大小: " + size + "\n");
   }
}

9.Java 实例 – 只读集合

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
 
public class Main {
    
    
   public static void main(String[] argv) 
   throws Exception {
    
    
      List stuff = Arrays.asList(new String[] {
    
     "a", "b" });
      List list = new ArrayList(stuff);
      list = Collections.unmodifiableList(list);
      try {
    
    
         list.set(0, "new value");
      } 
        catch (UnsupportedOperationException e) {
    
    
      }
      Set set = new HashSet(stuff);
      set = Collections.unmodifiableSet(set);
      Map map = new HashMap();
      map = Collections.unmodifiableMap(map);
      System.out.println("集合现在是只读");
   }
}

10.Java 实例 – 集合输出

import java.util.*;
 
public class Main{
    
    
   public static void main(String[] args) {
    
    
      System.out.println("TreeMap 实例！\n");
      TreeMap tMap = new TreeMap();
      tMap.put(1, "Sunday");
      tMap.put(2, "Monday");
      tMap.put(3, "Tuesday");
      tMap.put(4, "Wednesday");
      tMap.put(5, "Thursday");
      tMap.put(6, "Friday");
      tMap.put(7, "Saturday");
      System.out.println("TreeMap 键：" 
      + tMap.keySet());
      System.out.println("TreeMap 值：" 
      + tMap.values());
      System.out.println("键为 5 的值为: " + tMap.get(5)+ "\n");
      System.out.println("第一个键: " + tMap.firstKey() 
      + " Value: " 
      + tMap.get(tMap.firstKey()) + "\n");
      System.out.println("最后一个键: " + tMap.lastKey() 
      + " Value: "+ tMap.get(tMap.lastKey()) + "\n");
      System.out.println("移除第一个数据: " 
      + tMap.remove(tMap.firstKey()));
      System.out.println("现在 TreeMap 键为: " 
      + tMap.keySet());
      System.out.println("现在 TreeMap 包含: " 
      + tMap.values() + "\n");
      System.out.println("移除最后一个数据: " 
      + tMap.remove(tMap.lastKey()));
      System.out.println("现在 TreeMap 键为: " 
      + tMap.keySet());
      System.out.println("现在 TreeMap 包含: " 
      + tMap.values());
   }
}

11.Java 实例 – 集合转数组

import java.util.*;
 
public class Main{
    
    
   public static void main(String[] args){
    
    
      List<String> list = new ArrayList<String>();
      list.add("菜"); 
      list.add("鸟"); 
      list.add("教");
      list.add("程");
      list.add("www.runoob.com");
      String[] s1 = list.toArray(new String[0]); 
      for(int i = 0; i < s1.length; ++i){
    
    
         String contents = s1[i];
         System.out.print(contents);
     } 
   }
}

12.Java 实例 – List 循环移动元素

import java.util.*;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      List list = Arrays.asList("one Two three Four five six".split(" "));
      System.out.println("List :"+list);
      Collections.rotate(list, 3);
      System.out.println("rotate: " + list);
   }
}

13.Java 实例 – 查找 List 中的最大最小值

import java.util.*;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      List list = Arrays.asList("one Two three Four five six one three Four".split(" "));
      System.out.println(list);
      System.out.println("最大值: " + Collections.max(list));
      System.out.println("最小值: " + Collections.min(list));
   }
}

14.Java 实例 – 遍历 HashTable 的键值

import java.util.Enumeration;
import java.util.Hashtable;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      Hashtable ht = new Hashtable();
      ht.put("1", "One");
      ht.put("2", "Two");
      ht.put("3", "Three");
      Enumeration e = ht.keys();
      while (e.hasMoreElements()){
    
    
         System.out.println(e.nextElement());
      }
   }
}

15.Java 实例 – 使用 Enumeration 遍历 HashTable

import java.util.Enumeration;
import java.util.Hashtable;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      Hashtable ht = new Hashtable();
      ht.put("1", "One");
      ht.put("2", "Two");
      ht.put("3", "Three");
      Enumeration e = ht.elements();
      while(e.hasMoreElements()){
    
    
         System.out.println(e.nextElement());
      }
   }
}

16.Java 实例 – 集合中添加不同类型元素

import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;
 
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
 
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      List lnkLst = new LinkedList();
      lnkLst.add("element1");
      lnkLst.add("element2");
      lnkLst.add("element3");
      lnkLst.add("element4");
      displayAll(lnkLst);
      List aryLst = new ArrayList();
      aryLst.add("x");
      aryLst.add("y");
      aryLst.add("z");
      aryLst.add("w");
      displayAll(aryLst);
      Set hashSet = new HashSet();
      hashSet.add("set1");
      hashSet.add("set2");
      hashSet.add("set3");
      hashSet.add("set4");
      displayAll(hashSet);
      SortedSet treeSet = new TreeSet();
      treeSet.add("1");
      treeSet.add("2");
      treeSet.add("3");
      treeSet.add("4");
      displayAll(treeSet);
      LinkedHashSet lnkHashset = new LinkedHashSet();
      lnkHashset.add("one");
      lnkHashset.add("two");
      lnkHashset.add("three");
      lnkHashset.add("four");
      displayAll(lnkHashset);
      Map map1 = new HashMap();
      map1.put("key1", "J");
      map1.put("key2", "K");
      map1.put("key3", "L");
      map1.put("key4", "M");
      displayAll(map1.keySet());
      displayAll(map1.values());
      SortedMap map2 = new TreeMap();
      map2.put("key1", "JJ");
      map2.put("key2", "KK");
      map2.put("key3", "LL");
      map2.put("key4", "MM");
      displayAll(map2.keySet());
      displayAll(map2.values());
      LinkedHashMap map3 = new LinkedHashMap();
      map3.put("key1", "JJJ");
      map3.put("key2", "KKK");
      map3.put("key3", "LLL");
      map3.put("key4", "MMM");
      displayAll(map3.keySet());
      displayAll(map3.values());
   }
   static void displayAll(Collection col) {
    
    
      Iterator itr = col.iterator();
      while (itr.hasNext()) {
    
    
         String str = (String) itr.next();
         System.out.print(str + " ");
      }
      System.out.println();
   }
}

17.Java 实例 – List 元素替换

import java.util.*;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      List list = Arrays.asList("one Two three Four five six one three Four".split(" "));
      System.out.println("List :"+list);
      Collections.replaceAll(list, "one", "hundrea");
      System.out.println("replaceAll: " + list);
   }
}

18.Java 实例 – List 截取

import java.util.*;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      List list = Arrays.asList("one Two three Four five six one three Four".split(" "));
      System.out.println("List :"+list);
      List sublist = Arrays.asList("three Four".split(" "));
      System.out.println("子列表 :"+sublist);
      System.out.println("indexOfSubList: "
      + Collections.indexOfSubList(list, sublist));
      System.out.println("lastIndexOfSubList: "
      + Collections.lastIndexOfSubList(list, sublist));
   }
}

十一.Java 网络实例

1.Java 实例 – 获取指定主机的IP地址

import java.net.InetAddress;
import java.net.UnknownHostException;
 
public class GetIP {
    
    
    public static void main(String[] args) {
    
    
        InetAddress address = null;
        try {
    
    
            address = InetAddress.getByName("www.runoob.com");
        }
        catch (UnknownHostException e) {
    
    
            System.exit(2);
        }
        System.out.println(address.getHostName() + "=" + address.getHostAddress());
        System.exit(0);
    }
}

2.Java 实例 – 查看端口是否已使用

import java.net.*;
import java.io.*;
 
public class Main {
    
    
   public static void main(String[] args) {
    
    
      Socket Skt;
      String host = "localhost";
      if (args.length > 0) {
    
    
         host = args[0];
      }
      for (int i = 0; i < 1024; i++) {
    
    
         try {
    
    
            System.out.println("查看 "+ i);
            Skt = new Socket(host, i);
            System.out.println("端口 " + i + " 已被使用");
         }
         catch (UnknownHostException e) {
    
    
            System.out.println("Exception occured"+ e);
            break;
         }
         catch (IOException e) {
    
    
         }
      }
   }
}

3.Java 实例 – 获取本机ip地址及主机名

import java.net.InetAddress;
import java.net.UnknownHostException;
 
public class NetworkInfo {
    
    
    public static void main(String[] args) {
    
    
        try {
    
    
            // 获取本地主机对象
            InetAddress localHost = InetAddress.getLocalHost();
            
            // 获取主机名
            String hostName = localHost.getHostName();
            System.out.println("主机名: " + hostName);
            
            // 获取IP地址
            String hostAddress = localHost.getHostAddress();
            System.out.println("IP地址: " + hostAddress);
        } catch (UnknownHostException e) {
    
    
            System.err.println("无法获取本机IP地址及主机名: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

4.Java 实例 – 获取远程文件大小

import java.net.URL;
import java.net.URLConnection;
 
public class Main {
    
    
   public static void main(String[] args) throws Exception {
    
    
      int size;
      URL url = new URL("http://www.runoob.com/wp-content/themes/runoob/assets/img/newlogo.png");
      URLConnection conn = url.openConnection();
      size = conn.getContentLength();
      if (size < 0)
          System.out.println("无法获取文件大小。");
      else
        System.out.println("文件大小为：" + size + " bytes");
      conn.getInputStream().close();
   }
}

5.Java 实例 – Socket 实现多线程服务器程序

import java.io.*;
import java.net.*;
 
public class MultiThreadedServer {
    
    
    public static void main(String[] args) {
    
    
        int port = 12345; // 定义服务器端口
        try (ServerSocket serverSocket = new ServerSocket(port)) {
    
    
            System.out.println("服务器已启动，等待客户端连接...");
 
            while (true) {
    
    
                Socket clientSocket = serverSocket.accept(); // 接受客户端连接
                System.out.println("客户端已连接: " + clientSocket.getInetAddress().getHostAddress());
 
                // 为每个客户端连接启动一个新的线程
                ClientHandler clientHandler = new ClientHandler(clientSocket);
                new Thread(clientHandler).start();
            }
        } catch (IOException e) {
    
    
            e.printStackTrace();
        }
    }
}
 
class ClientHandler implements Runnable {
    
    
    private Socket clientSocket;
 
    public ClientHandler(Socket socket) {
    
    
        this.clientSocket = socket;
    }
 
    @Override
    public void run() {
    
    
        try (
            InputStream input = clientSocket.getInputStream();
            OutputStream output = clientSocket.getOutputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(input));
            PrintWriter writer = new PrintWriter(output, true)
        ) {
    
    
            String clientMessage;
            while ((clientMessage = reader.readLine()) != null) {
    
    
                System.out.println("收到客户端消息: " + clientMessage);
                writer.println("服务器回应: " + clientMessage); // 发送回应消息给客户端
            }
        } catch (IOException e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            try {
    
    
                clientSocket.close();
            } catch (IOException e) {
    
    
                e.printStackTrace();
            }
        }
    }
}

6.Java 实例 – 查看主机指定文件的最后修改时间

import java.net.URL;
import java.net.URLConnection;
import java.util.Date;
import java.text.SimpleDateFormat;
 
public class Main {
    
    
    public static void main(String[] argv) throws Exception {
    
    
        URL u = new URL("http://127.0.0.1/test/test.html");
        URLConnection uc = u.openConnection();
        SimpleDateFormat ft = new SimpleDateFormat ("yyyy-MM-dd hh:mm:ss");
        uc.setUseCaches(false);
        long timestamp = uc.getLastModified();
        System.out.println("test.html 文件最后修改时间 :" + ft.format(new Date(timestamp)));
    }
}

7.Java 实例 – 使用 Socket 连接到指定主机

import java.net.InetAddress;
import java.net.Socket;
 
public class WebPing {
    
    
    public static void main(String[] args) {
    
    
        try {
    
    
            InetAddress addr;
            Socket sock = new Socket("www.runoob.com", 80);
            addr = sock.getInetAddress();
            System.out.println("连接到 " + addr);
            sock.close();
        } catch (java.io.IOException e) {
    
    
            System.out.println("无法连接 " + args[0]);
            System.out.println(e);
        }
    }
}

8.Java 实例 – 网页抓取

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.InputStreamReader;
import java.net.URL;
 
public class Main {
    
    
   public static void main(String[] args) 
   throws Exception {
    
    
      URL url = new URL("http://www.runoob.com");
      BufferedReader reader = new BufferedReader
      (new InputStreamReader(url.openStream()));
      BufferedWriter writer = new BufferedWriter
      (new FileWriter("data.html"));
      String line;
      while ((line = reader.readLine()) != null) {
    
    
         System.out.println(line);
         writer.write(line);
         writer.newLine();
      }
      reader.close();
      writer.close();
   }
}

9.Java 实例 – 获取 URL响应头的日期信息

import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Date;
 
public class Main{
    
    
   public static void main(String args[]) 
   throws Exception {
    
    
      URL url = new URL("http://www.runoob.com");
      HttpURLConnection httpCon = 
      (HttpURLConnection) url.openConnection();
      long date = httpCon.getDate();
      if (date == 0)
      System.out.println("无法获取信息。");
      else
      System.out.println("Date: " + new Date(date));
   }
}

10.Java 实例 – 获取 URL 响应头信息

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Map;
import java.util.Set;
 
public class Main {
    
    
    public static void main(String[] args) throws IOException{
    
    
        URL url = new URL("http://www.runoob.com");
        URLConnection conn = url.openConnection();
        
        Map headers = conn.getHeaderFields();
        Set<String> keys = headers.keySet();
        for( String key : keys ){
    
    
            String val = conn.getHeaderField(key);
            System.out.println(key+"    "+val);
        }
        System.out.println( conn.getLastModified() );
    }
}

11.Java 实例 – 解析 URL

import java.net.URL;
 
public class Main {
    
    
   public static void main(String[] args) 
   throws Exception {
    
    
      URL url = new URL("http://www.runoob.com/html/html-tutorial.html");
      System.out.println("URL 是 " + url.toString());
      System.out.println("协议是 " + url.getProtocol());
      System.out.println("文件名是 " + url.getFile());
      System.out.println("主机是 " + url.getHost());
      System.out.println("路径是 " + url.getPath());
      System.out.println("端口号是 " + url.getPort());
      System.out.println("默认端口号是 " 
      + url.getDefaultPort());
   }
}

12.Java 实例 – ServerSocket 和 Socket 通信实例

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
 
public class Server {
    
    
   public static void main(String[] args) {
    
    
      try {
    
    
         ServerSocket ss = new ServerSocket(8888);
         System.out.println("启动服务器....");
         Socket s = ss.accept();
         System.out.println("客户端:"+s.getInetAddress().getLocalHost()+"已连接到服务器");
         
         BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
         //读取客户端发送来的消息
         String mess = br.readLine();
         System.out.println("客户端："+mess);
         BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
         bw.write(mess+"\n");
         bw.flush();
      } catch (IOException e) {
    
    
         e.printStackTrace();
      }
   }
}

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.Socket;
import java.net.UnknownHostException;
 
public class Client {
    
    
   public static void main(String[] args) {
    
    
      try {
    
    
         Socket s = new Socket("127.0.0.1",8888);
         
         //构建IO
         InputStream is = s.getInputStream();
         OutputStream os = s.getOutputStream();
         
         BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os));
         //向服务器端发送一条消息
         bw.write("测试客户端和服务器通信，服务器接收到消息返回到客户端\n");
         bw.flush();
         
         //读取服务器返回的消息
         BufferedReader br = new BufferedReader(new InputStreamReader(is));
         String mess = br.readLine();
         System.out.println("服务器："+mess);
      } catch (UnknownHostException e) {
    
    
         e.printStackTrace();
      } catch (IOException e) {
    
    
         e.printStackTrace();
      }
   }
}

十二.Java 线程

1.Java 实例 – 查看线程是否存活

public class TwoThreadAlive extends Thread {
    
    
   public void run() {
    
    
      for (int i = 0; i < 10; i++) {
    
    
         printMsg();
      }
   }
 
   public void printMsg() {
    
    
      Thread t = Thread.currentThread();
      String name = t.getName();
      System.out.println("name=" + name);
   }
 
   public static void main(String[] args) {
    
    
      TwoThreadAlive tt = new TwoThreadAlive();
      tt.setName("Thread");
      System.out.println("before start(), tt.isAlive()=" + tt.isAlive());
      tt.start();
      System.out.println("just after start(), tt.isAlive()=" + tt.isAlive());
      for (int i = 0; i < 10; i++) {
    
    
         tt.printMsg();
      }
      System.out.println("The end of main(), tt.isAlive()=" + tt.isAlive());
   }
}

2.Java 实例 – 获取当前线程名称

public class TwoThreadGetName extends Thread {
    
    
   public void run() {
    
    
      for (int i = 0; i < 10; i++) {
    
    
         printMsg();
      }
   }
   public void printMsg() {
    
    
      Thread t = Thread.currentThread();
      String name = t.getName();
      System.out.println("name=" + name);
   } 
   public static void main(String[] args) {
    
    
      TwoThreadGetName tt = new TwoThreadGetName();
      tt.start();
      for (int i = 0; i < 10; i++) {
    
    
         tt.printMsg();
      }
   }
}

3.Java 实例 – 状态监测

class MyThread extends Thread{
    
    
   boolean waiting= true;
   boolean ready= false;
   MyThread() {
    
    
   }
   public void run() {
    
    
      String thrdName = Thread.currentThread().getName();
      System.out.println(thrdName + " starting.");
      while(waiting) 
      System.out.println("waiting:"+waiting); 
      System.out.println("waiting...");
      startWait(); 
      try {
    
    
         Thread.sleep(1000);
      }
      catch(Exception exc) {
    
    
         System.out.println(thrdName + " interrupted.");
      }
      System.out.println(thrdName + " terminating.");
   }
   synchronized void startWait() {
    
    
      try {
    
    
         while(!ready) wait();
      }
      catch(InterruptedException exc) {
    
    
         System.out.println("wait() interrupted");
      }
   }
   synchronized void notice() {
    
    
      ready = true;
      notify();
   }
}
public class Main {
    
    
   public static void main(String args[]) 
   throws Exception{
    
    
      MyThread thrd = new MyThread();
      thrd.setName("MyThread #1");
      showThreadStatus(thrd);
      thrd.start();
      Thread.sleep(50);
      showThreadStatus(thrd);
      thrd.waiting = false;
      Thread.sleep(50); 
      showThreadStatus(thrd);
      thrd.notice();
      Thread.sleep(50);
      showThreadStatus(thrd);
      while(thrd.isAlive()) 
      System.out.println("alive");
      showThreadStatus(thrd);
   }
   static void showThreadStatus(Thread thrd) {
    
    
      System.out.println(thrd.getName() + "Alive:=" + thrd.isAlive() + " State:=" + thrd.getState());
   }
}

4.Java 实例 – 线程优先级设置

public class SimplePriorities extends Thread {
    
    
   private int countDown = 5;
   private volatile double d = 0; 
   public SimplePriorities(int priority) {
    
    
      setPriority(priority);
      start();
   }
   public String toString() {
    
    
      return super.toString() + ": " + countDown;
   }
   public void run() {
    
    
      while(true) {
    
    
         for(int i = 1; i < 100000; i++)
         d = d + (Math.PI + Math.E) / (double)i;
         System.out.println(this);
         if(--countDown == 0) return;
      }
   }
   public static void main(String[] args) {
    
    
      new SimplePriorities(Thread.MAX_PRIORITY);
      for(int i = 0; i < 5; i++)
      new SimplePriorities(Thread.MIN_PRIORITY);
   }
}

5.Java 实例 – 死锁及解决方法

import java.util.Date;
 
public class LockTest {
    
    
   public static String obj1 = "obj1";
   public static String obj2 = "obj2";
   public static void main(String[] args) {
    
    
      LockA la = new LockA();
      new Thread(la).start();
      LockB lb = new LockB();
      new Thread(lb).start();
   }
}
class LockA implements Runnable{
    
    
   public void run() {
    
    
      try {
    
    
         System.out.println(new Date().toString() + " LockA 开始执行");
         while(true){
    
    
            synchronized (LockTest.obj1) {
    
    
               System.out.println(new Date().toString() + " LockA 锁住 obj1");
               Thread.sleep(3000); // 此处等待是给B能锁住机会
               synchronized (LockTest.obj2) {
    
    
                  System.out.println(new Date().toString() + " LockA 锁住 obj2");
                  Thread.sleep(60 * 1000); // 为测试，占用了就不放
               }
            }
         }
      } catch (Exception e) {
    
    
         e.printStackTrace();
      }
   }
}
class LockB implements Runnable{
    
    
   public void run() {
    
    
      try {
    
    
         System.out.println(new Date().toString() + " LockB 开始执行");
         while(true){
    
    
            synchronized (LockTest.obj2) {
    
    
               System.out.println(new Date().toString() + " LockB 锁住 obj2");
               Thread.sleep(3000); // 此处等待是给A能锁住机会
               synchronized (LockTest.obj1) {
    
    
                  System.out.println(new Date().toString() + " LockB 锁住 obj1");
                  Thread.sleep(60 * 1000); // 为测试，占用了就不放
               }
            }
         }
      } catch (Exception e) {
    
    
         e.printStackTrace();
      }
   }
}

6.Java 实例 – 获取线程id

public class Main extends Object implements Runnable {
    
    
  private ThreadID var;
 
  public Main(ThreadID v) {
    
    
    this.var = v;
  }
 
  public void run() {
    
    
    try {
    
    
      print("var getThreadID =" + var.getThreadID());
      Thread.sleep(2000);
      print("var getThreadID =" + var.getThreadID());
    } catch (InterruptedException x) {
    
    
    }
  }
 
  private static void print(String msg) {
    
    
    String name = Thread.currentThread().getName();
    System.out.println(name + ": " + msg);
  }
 
  public static void main(String[] args) {
    
    
    ThreadID tid = new ThreadID();
    Main shared = new Main(tid);
 
    try {
    
    
      Thread threadA = new Thread(shared, "threadA");
      threadA.start();
 
      Thread.sleep(500);
 
      Thread threadB = new Thread(shared, "threadB");
      threadB.start();
 
      Thread.sleep(500);
 
      Thread threadC = new Thread(shared, "threadC");
      threadC.start();
    } catch (InterruptedException x) {
    
    
    }
  }
}
 
class ThreadID extends ThreadLocal {
    
    
  private int nextID;
 
  public ThreadID() {
    
    
    nextID = 10001;
  }
 
  private synchronized Integer getNewID() {
    
    
    Integer id = new Integer(nextID);
    nextID++;
    return id;
  }
 
 
  protected Object initialValue() {
    
    
    print("in initialValue()");
    return getNewID();
  }
 
  public int getThreadID() {
    
    
    Integer id = (Integer) get();
    return id.intValue();
  }
 
  private static void print(String msg) {
    
    
    String name = Thread.currentThread().getName();
    System.out.println(name + ": " + msg);
  }
}

7.Java 实例 – 线程挂起

public class SleepingThread extends Thread {
    
    
   private int countDown = 5;
   private static int threadCount = 0;
   public SleepingThread() {
    
    
      super("" + ++threadCount);
      start();
   }
   public String toString() {
    
     
      return "#" + getName() + ": " + countDown;
   }
   public void run() {
    
    
      while (true) {
    
    
         System.out.println(this);
         if (--countDown == 0)
            return;
         try {
    
    
            sleep(100);
         }
         catch (InterruptedException e) {
    
    
            throw new RuntimeException(e);
         }
      }
   }
   public static void main(String[] args) 
   throws InterruptedException {
    
    
      for (int i = 0; i < 5; i++)
      new SleepingThread().join();
      System.out.println("线程已被挂起");
   }
}

8.Java 实例 – 终止线程

public class ThreadInterrupt extends Thread 
{
    
     
    public void run() 
    {
    
     
        try 
        {
    
     
            sleep(50000);  // 延迟50秒 
        } 
        catch (InterruptedException e) 
        {
    
     
            System.out.println(e.getMessage()); 
        } 
    } 
    public static void main(String[] args) throws Exception 
    {
    
     
        Thread thread = new ThreadInterrupt(); 
        thread.start(); 
        System.out.println("在50秒之内按任意键中断线程!"); 
        System.in.read(); 
        thread.interrupt(); 
        thread.join(); 
        System.out.println("线程已经退出!"); 
    } 
}

9.Java 实例 – 生产者/消费者问题

/*
 author by runoob.com
 ProducerConsumerTest.java
 */

public class ProducerConsumerTest {
    
    
   public static void main(String[] args) {
    
    
      CubbyHole c = new CubbyHole();
      Producer p1 = new Producer(c, 1);
      Consumer c1 = new Consumer(c, 1);
      p1.start(); 
      c1.start();
   }
}
class CubbyHole {
    
    
   private int contents;
   private boolean available = false;
   public synchronized int get() {
    
    
      while (available == false) {
    
    
         try {
    
    
            wait();
         }
         catch (InterruptedException e) {
    
    
         }
      }
      available = false;
      notifyAll();
      return contents;
   }
   public synchronized void put(int value) {
    
    
      while (available == true) {
    
    
         try {
    
    
            wait();
         }
         catch (InterruptedException e) {
    
     
         } 
      }
      contents = value;
      available = true;
      notifyAll();
   }
}

class Consumer extends Thread {
    
    
   private CubbyHole cubbyhole;
   private int number;
   public Consumer(CubbyHole c, int number) {
    
    
      cubbyhole = c;
      this.number = number;
   }
   public void run() {
    
    
      int value = 0;
         for (int i = 0; i < 10; i++) {
    
    
            value = cubbyhole.get();
            System.out.println("消费者 #" + this.number+ " got: " + value);
         }
    }
}

class Producer extends Thread {
    
    
   private CubbyHole cubbyhole;
   private int number;

   public Producer(CubbyHole c, int number) {
    
    
      cubbyhole = c;
      this.number = number;
   }

   public void run() {
    
    
      for (int i = 0; i < 10; i++) {
    
    
         cubbyhole.put(i);
         System.out.println("生产者 #" + this.number + " put: " + i);
         try {
    
    
            sleep((int)(Math.random() * 100));
         } catch (InterruptedException e) {
    
     }
      }
   }
}

10.Java 实例 – 获取线程状态

// Java 程序 - 演示线程状态
class thread implements Runnable 
{
    
     
    public void run() 
    {
    
     
        //  thread2  - 超时等待
        try
        {
    
     
            Thread.sleep(1500); 
        }  
        catch (InterruptedException e)  
        {
    
     
            e.printStackTrace(); 
        } 
          
        System.out.println("State of thread1 while it called join() method on thread2 -"+ 
            Test.thread1.getState()); 
        try
        {
    
     
            Thread.sleep(200); 
        }  
        catch (InterruptedException e)  
        {
    
     
            e.printStackTrace(); 
        }      
    } 
} 
  
public class Test implements Runnable 
{
    
     
    public static Thread thread1; 
    public static Test obj; 
      
    public static void main(String[] args) 
    {
    
     
        obj = new Test(); 
        thread1 = new Thread(obj); 
          
        // 创建 thread1，现在是初始状态
        System.out.println("State of thread1 after creating it - " + thread1.getState()); 
        thread1.start(); 
          
        // thread1 - 就绪状态
        System.out.println("State of thread1 after calling .start() method on it - " +  
            thread1.getState()); 
    } 
      
    public void run() 
    {
    
     
        thread myThread = new thread(); 
        Thread thread2 = new Thread(myThread); 
          
        // 创建 thread1，现在是初始状态
        System.out.println("State of thread2 after creating it - "+ thread2.getState()); 
        thread2.start(); 
          
        // thread2 - 就绪状态
        System.out.println("State of thread2 after calling .start() method on it - " +  
            thread2.getState()); 
          
        // moving thread1 to timed waiting state 
        try
        {
    
     
            //moving - 超时等待
            Thread.sleep(200); 
        }  
        catch (InterruptedException e)  
        {
    
     
            e.printStackTrace(); 
        } 
        System.out.println("State of thread2 after calling .sleep() method on it - "+  
            thread2.getState() ); 
          
          
        try 
        {
    
     
            // 等待 thread2 终止
            thread2.join(); 
        }  
        catch (InterruptedException e)  
        {
    
     
            e.printStackTrace(); 
        } 
        System.out.println("State of thread2 when it has finished it's execution - " +  
            thread2.getState()); 
    } 
      
}

11.Java 实例 – 获取所有线程

public class Main extends Thread {
    
    
   public static void main(String[] args) {
    
    
      Main t1 = new Main();
      t1.setName("thread1");
      t1.start();
      ThreadGroup currentGroup = 
      Thread.currentThread().getThreadGroup();
      int noThreads = currentGroup.activeCount();
      Thread[] lstThreads = new Thread[noThreads];
      currentGroup.enumerate(lstThreads);
      for (int i = 0; i < noThreads; i++)
      System.out.println("线程号：" + i + " = " + lstThreads[i].getName());
   }
}

12.Java 实例 – 查看线程优先级

public class Main extends Object {
    
    
   private static Runnable makeRunnable() {
    
    
      Runnable r = new Runnable() {
    
    
         public void run() {
    
    
            for (int i = 0; i < 5; i++) {
    
    
               Thread t = Thread.currentThread();
               System.out.println("in run() - priority="
               + t.getPriority()+ ", name=" + t.getName());
               try {
    
    
                  Thread.sleep(2000);
               }
               catch (InterruptedException x) {
    
    
               }
            }
         }
      };
      return r;
   }
   public static void main(String[] args) {
    
    
      System.out.println("in main() - Thread.currentThread().getPriority()=" + Thread.currentThread().getPriority());
      System.out.println("in main() - Thread.currentThread().getName()="+ Thread.currentThread().getName());
      Thread threadA = new Thread(makeRunnable(), "threadA");
      threadA.start();
      try {
    
    
         Thread.sleep(3000);
      }
      catch (InterruptedException x) {
    
    
      }
      System.out.println("in main() - threadA.getPriority()="+ threadA.getPriority());
   }
}

13.Java 实例 – 中断线程

public class Main extends Object 
implements Runnable {
    
    
   public void run() {
    
    
      try {
    
    
         System.out.println("in run() - 将运行 work2() 方法");
         work2();
         System.out.println("in run() - 从 work2() 方法回来");
      }
      catch (InterruptedException x) {
    
    
         System.out.println("in run() - 中断 work2() 方法");
         return;
      }
      System.out.println("in run() - 休眠后执行");
      System.out.println("in run() - 正常离开");
   }
   public void work2() throws InterruptedException {
    
    
      while (true) {
    
    
         if (Thread.currentThread().isInterrupted()) {
    
    
            System.out.println("C isInterrupted()=" + Thread.currentThread().isInterrupted());
            Thread.sleep(2000);
            System.out.println("D isInterrupted()=" + Thread.currentThread().isInterrupted());
         }
      }
   }
   public void work() throws InterruptedException {
    
    
      while (true) {
    
    
         for (int i = 0; i < 100000; i++) {
    
    
            int j = i * 2;
         }
         System.out.println("A isInterrupted()=" + Thread.currentThread().isInterrupted());
         if (Thread.interrupted()) {
    
    
            System.out.println("B isInterrupted()=" + Thread.currentThread().isInterrupted());
            throw new InterruptedException();
         }
      }
   }
   public static void main(String[] args) {
    
    
      Main si = new Main();
      Thread t = new Thread(si);
      t.start();
      try {
    
    
         Thread.sleep(2000);
      }
      catch (InterruptedException x) {
    
    
      }
      System.out.println("in main() - 中断其他线程");
      t.interrupt();
      System.out.println("in main() - 离开");
   }
}