String类

常用方法

public class test1 {
    public static void main(String[] args) {
    String a = "Hello World";
    String b = "Hello Java";
        System.out.println(a.length());             // 返回字符串长度
        System.out.println(a.charAt(1));            // 返回索引处的字符
        System.out.println(a.isEmpty());            // 是否为空字符
        System.out.println(a.toLowerCase());        // 将字符转为小写
        System.out.println(a.toUpperCase());        // 将字符转为大写
        System.out.println(a.trim());               // 获取字符串副本,并且删除空格
        System.out.println(a.equals(b));            // 比较字符串内容是否相同
        System.out.println(a.equalsIgnoreCase(b));  // 比较字符串内容是否相同,忽略大小写
        System.out.println(a.concat(b));            // 将指定字符串连接到此字符串的结尾
        System.out.println(a.compareTo(b));         // 比较两个字符串的大小
        System.out.println(a.substring(0,2));       // 返回一个新字符串从0截取到2如果只有一个参数则从参数截取到最后
        System.out.println(a.startsWith(b));        //判断字符串a是否以字符串b为开头
        System.out.println(a.endsWith(b));          //判断字符串a是否以字符串b为结尾
        System.out.println(a.contains(b));          //判断字符串a是否包含字符串b
        System.out.println(a.indexOf(b));           //判断字符串a中字符串b是否存在并返回索引
        System.out.println(a.replace("World","java"));   //将字符串中World替换成java
        System.out.println(a.replaceAll("H.*?d",","));   //使用正则替换
        System.out.println(a.matches(".*?"));   //判断字符串是否符合正则
        System.out.println(a.split(" "));     //根据正则将字符串切片成数组
    }
}
/*
11
e
false
hello world
HELLO WORLD
Hello World
false
false
Hello WorldHello Java
13
He
false
false
false
-1
Hello java
,
true
[Ljava.lang.String;@1b6d3586
Process finished with exit code 0
*/

String 转换成其他类型

public class test1 {
    public static void main(String[] args) {
    String a = "221";
        System.out.println(Integer.parseInt(a));
    }
}
// 类型.parsexxx()

String 转成字节数组

public class test1 {
    public static void main(String[] args) {
    String a = "221";
    String b = "Hello Java";
    byte []c = b.getBytes();
        System.out.println(Arrays.toString(c));
    }
}
//设置编码集为gbk
public class test1 {
    public static void main(String[] args) throws UnsupportedEncodingException {
    String a = "221";
    String b = "Hello Java";
    byte []c = b.getBytes("gbk");
        System.out.println(Arrays.toString(c));
    }
}
//字节转成String时设置编码集
String d  = new String(c,"gbk");

StringBuffer

public class test1 {
    public static void main(String[] args){
    StringBuffer a= new StringBuffer("HelloWorld");
    a.setCharAt(0,'2');              //将索引为1的字符改为2
    a.append('1');                   //在当前字符串后面增加1
    a.delete(0,1);                   //删除索引0-1之间的字符
    a.replace(0,1,"a");              //将索引0-1字符替换成a
    a.insert(0,"ada");               //在指定位置增加字符
    a.reverse();                     //将当前字符逆转
    System.out.println(a.charAt(1)); //查询索引1处的字符
    }
}