The use of StringBuffer and StringBuilder and the difference with String

Use of StringBuilder:

package class01.object01;

/**
 *
 * @create 2021-02-24 14:54
 * StringBuffer和StringBuilder的使用
 * 和String区别：效率比String高；比String节省内存
 */
public class Demo04 {
    
    
    public static void main(String[] args) {
    
    
        StringBuffer sb=new StringBuffer();
        // apend()追加
        sb.append("Java世界第一");
        System.out.println(sb.toString());
        sb.append("Java真香");
        System.out.println(sb.toString());
        sb.append("Java不错");
        // insert() 添加
        sb.insert(0,"我在最前面");
        System.out.println(sb.toString());
        // replace; 替换
        sb.replace(0,5,"hello");
        System.out.println(sb);
        //delete(); 删除
        sb.delete(0,5);
        System.out.println(sb);
        //清空
        sb.delete(0,sb.length());
        System.out.println(sb.length());
    }
}

Difference with String: higher efficiency than String; save memory than String

package class01.object01;

/**
 * 
 * @create 2021-02-24 15:09
 */
public class Demo05 {
    
    
    public static void main(String[] args) {
    
    
        //开始时间
        long start = System.currentTimeMillis();

        /*String string="";

        for(int i =0;i<99999;i++){
            string+=i;}
            System.out.println(string);*/
        StringBuilder sb= new StringBuilder();
        for(int i =0;i<99999;i++){
    
    
            sb.append(i);}
        System.out.println(sb.toString());
            long end=System.currentTimeMillis();
            System.out.println("用时"+(end-start));

    }
}