一些常用的API

常用api
(1) char charAt(int index)
(2) char[] toCharArray()
(3) boolean equals(String)
(4) String substring(int start, int end)
(5) String substring(int start)
(6) boolean startsWith(String)
– 从offset位置开始, 是否以指定字符串打头
(7) boolean startsWith(String, int offset)
(8) boolean endsWith(String)
(9) int indexOf(char)
int indexOf(String)
– 从fromIndex开始往后, 第一次出现char的位置
int indexOf(char, int fromIndex)
int indexOf(String, int fromIndex)
int length()
(10)boolean equalsIgnoreCase(String)
– 去掉字符串左右两边的空白字符
(11) String trim()

public class Num6 {
    public static void main(String args[]) {
        String s = "www.runoob.com";
        char result = s.charAt(6);
        //输出结果为"n"
        System.out.println(result);
    }
}

import java.util.Arrays;

public class Num03 {
    public static void main(String[] args) {
        String s="+88 hello .com";
        //1.获得某一个下标对应的字符-->charAt()
        char c=s.charAt(0);
        System.out.println(c);
        String s1=new String();
        //2.字符串不能用s==s1类比较--->equals();
        boolean b=s1.equals(s);//s.equals(s1)
        System.out.println("equals: "+b);
        //忽略大小写比较--->equalsIgnoreCase();
        boolean b1=s1.equalsIgnoreCase(s);
        //3.将字符串s转换成字符数组--->toCharArray();
        char[] chs=s.toCharArray();
        System.out.println("toCharArray: "+ Arrays.toString(chs));
        //4统计字符串的字符个数,长度--->length();
        int length =s.length();
        System.out.println("length: "+length);
        //5.判断是否以xx开头--->startsWith();
        boolean b11=s.startsWith("+88");
        System.out.println("startWith: "+b11);
        //6.判断是否以xx结尾---->endsWith();
        boolean b2=s.endsWith(".com");
        System.out.println("endsWith: "+b2);
        //7.获得字符串中指定字符首次出现的位置
        int index=s.indexOf('@');
        System.out.println("indexOf: "+index);
        //8.截取字符串,s本身没变
        String sub=s.substring(0,5);
        System.out.println("substring: "+sub);
        //-- 去掉字符串左右两边的空白字符--->String trim()
        String s3=("    sfbds    ");
        String s31=s3.trim();
        System.out.println(s31);
    }
}

输出结果如下:
+
equals: false
toCharArray: [+, 8, 8, , h, e, l, l, o, , ., c, o, m]
length: 14
startWith: true
endsWith: true
indexOf: -1
substring: +88 h
sfbds]