String字符串常用的API

==与equals的区别：

1.==

public class demo2 {
    public static void main(String[] args) {
        //==在判断基本数据类型时，比较的是值
        int a = 10;
        int b = 10;
        System.out.println(a==b);//true

        //==在判断引用数据类型时，比较的是地址值
        int[] arr1 = {1,2,3};
        int[] arr2 = {1,2,3};
        System.out.println(arr1==arr2);//false
    }
}

2.equals（区分大小写）与equalsIgnoreCase（不区分大小写）

public class demo3 {
    public static void main(String[] args) {
        String s1 = "abc";
        String s2 = "ABC";

        //equals区分大小写
        boolean equals = s1.equals(s2);
        System.out.println("equals = " + equals);//false

        //不区分大小写equalsIgnoreCase
        boolean b = s1.equalsIgnoreCase(s2);
        System.out.println("b = " + b);//true
       }
}

内存区：

根据索引获取字符串里的元素：charAt

public class demo4 {
    public static void main(String[] args) {
        String s ="abcdefg";

        //长度
        int a = s.length();
        System.out.println("a = " + a);//7

        //charAt(index)根据索引获取元素
        char c = s.charAt(0);
        System.out.println("c = " + c);//a
    }
}

将字符串转化为字符数组：toCharArray

public class demo7 {
    public static void main(String[] args) {
        String s = "qwer";

        //将字符串转为字符数组
        char[] arr = s.toCharArray();

        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }
    }
}

截取字符串：substring

public class demo8 {
    public static void main(String[] args) {
        String s = "qwerty";

        String s1 = s.substring(0,5);//从索引0开始截取，一直截取到4（含头不含尾）
        System.out.println("s1 = " + s1);//qwert


        String substring = s.substring(3);//从3开始截取，一直截取到末尾
        System.out.println("substring = " + substring);
    }
}

替换字符串：replace

public class demo10 {
    public static void main(String[] args) {
        String s = "qwerdfwe";

        //将we替换成*，替换
        String we = s.replace("we", "**");
        System.out.println(we);
    }
}

字符切割字符串：split

public class demo12 {
    public static void main(String[] args) {
        String s = "张三-12-武汉";

        //根据-切割
        String[] split = s.split("-");

        for (int i = 0; i < split.length; i++) {
            System.out.println(split[i]);
        }
    }
}