常用API（一）：StringBuilder (用StringBuilder操作字符串效率更高比String) StringBuffer（线程更安全） StringJoniner（比String

package com.itheima.StringBuilder1;

public class StringBuilder1 {
    public static void main(String[] args) {
        StringBuilder s=new StringBuilder();
        StringBuilder s1=new StringBuilder("pengsuoqun");//创建新字符串
        s1.append(12);
        s1.append("黑马");
        s1.append(true);//拼接各种数据

        System.out.println(s1);

        s1.reverse();//内容反转
        System.out.println(s1);

        String s3=s1.toString();//转字符串
        System.out.println(s3);
    }
}

测试StringBuilder性能与String的性能的代码，StringBuilder性能更强劲

package com.itheima.StringBuilder1;

public class StringBuilder1 {
    public static void main(String[] args) {
        //目标：掌握StringBuilder的好处
        //需求：要拼接100万次abc
        //先用tring测试看看性能
//        String s="";
//        for (int i = 0; i <1000000 ; i++) {
//            s=s+"abc";
//        }
//        System.out.println(s);

        StringBuilder s=new StringBuilder();
        for (int i = 0; i <1000000 ; i++) {
            s.append("abc");
        }
        System.out.println(s);
    }
}

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