Collection 接口
他有 add(element:Object):boolean
remove(element:Object):boolean
size();int
isEmpty();boolean
contains(element:Object):boolean
iterator():Iterator
List 线性表 主要实现的类是ArrayListLinkdList 以及早期的Vector
import java.util.*;
class TestList
{
public static void main(String[] args)
{
List<Photo> album=new LinkedList<>();//<>里面是什么 表示它就是什么的线性表
//尖括号这种表示较泛型
album.add(new Photo("one",new Date(),"classroom"));
album.add(new Photo("two",new Date(),"library"));
album.add(new Photo("three",new Date(),"gym"));
album.add(new Photo("three",new Date(),"dorm"));
Iterator<Photo> iterator=album.iterator();
while(iterator.hasNext())
{
Photo photo=iterator.next();
System.out.println(photo.toString());
}
for(Photo photo:album)
{
System.out.println(photo);
}
}
}
class Photo
{
String title;
Date date;
String memo;
Photo(String title,Date date,String memo)
{
this.title=title;
this.date=date;
this.memo=memo;
}
@Override
public String toString()
{
return title+"("+date+")"+memo;
}
}
输出
one(Fri Dec 20 21:10:35 CST 2019)classroom
two(Fri Dec 20 21:10:35 CST 2019)library
three(Fri Dec 20 21:10:35 CST 2019)gym
three(Fri Dec 20 21:10:35 CST 2019)dorm
one(Fri Dec 20 21:10:35 CST 2019)classroom
two(Fri Dec 20 21:10:35 CST 2019)library
three(Fri Dec 20 21:10:35 CST 2019)gym
three(Fri Dec 20 21:10:35 CST 2019)dorm
栈 通过下面程序可知道 这种数据结构后进先出
import java.util.*;
public class TestStack{
static String[] months= {
"January","Fabruary","March","April",
"May","June","July","August","September",
"October","November","December"};
public static void main(String[] args) {
Stack<String> stk=new Stack<>();
for(int i=0;i<months.length;i++)
stk.push(months[i]+" ");
System.out.println("stk = "+stk);
System.out.println("popping elements: ");
while(!stk.empty())
System.out.println(stk.pop());
}
}
队列Queue 重要的线性数据结构 先进先出 FIFO
import java.util.*;
class TestQueue{
public static void main(String[] args) {
Queue<Integer> q=new LinkedList<>();
for(int i=0;i<5;i++) {
q.offer(i);//offer入队的意思
//可以智能的把整形转换成Integer
}
while(!q.isEmpty())
System.out.println(q.poll());
}
}
输出结果可见是先进先出
几个早期的类或接口
Vector 现在多用ArrayList
Stack 现在多用LinkedList
Hashtable 现在多用HashMap
Enumeration 现在多用Iterator
Set 两个重要的实现 HashSet TreeSet TreeSet底层是用TreeMap来实现的
Set中对象不重复 hashCode()不等
package equals;
import java.util.*;
class TestSet
{
public static void main(String[] args) {
Set<String>set=new HashSet<String>();//建立一个哈希表
//Set<String> set=new TreeSet<String>();
set.add("Brazil");
set.add("Russia");
set.add("India");
set.add("China");
set.add("South Africa");
System.out.println(set.contains("China"));
for(String obj:set)
System.out.println(obj);//最后输出的时候,会发现和存储的顺序不一样
}
}
Map类 HashMap类 TreeMap类:用红黑树的算法
import java.util.*;
class TestMap
{
public static void main(String[] args) {
//Map<String,String> map=new HashMap<String,String>();
Map<String,String> map=new TreeMap<String,String>();
map.put("b","Brazil");
map.put("r","Russia");
map.put("i","India");
map.put("c","China");
map.put("k","South Africa");
System.out.println(map.get("c"));
//先输出 c对应的键值
for(String key:map.keySet())
System.out.println(key+":"+map.get(key));
//第一种遍历方法
for(String value:map.values())
System.out.println(value);
//只输出键值
for(Map.Entry<String, String>entry:map.entrySet())
System.out.println(entry.getKey()+":"+entry.getValue());
//第二种遍历方法 推荐 尤其是容量大的时候
Iterator it=map.entrySet().iterator();
while(it.hasNext()) {
Map.Entry<String, String> entry=(Map.Entry<String, String>)it.next();
System.out.println(entry.getKey()+":"+entry.getValue());
}
//第三种遍历方法
//先构造迭代器 然后用迭代器遍历
}
}