StringBuilder

 1 public class demo11 {
 2     public static void main(String[] args) {
 3         //StringBuilder可以看作为一个容器，创建之后里面内容可变
 4         //1.创建对象

 5         StringBuilder sb = new StringBuilder();
 6         //StringBuilder sb = new StringBuilder("abc");
 7 
 8         //2.添加元素
 9         sb.append("abc");
10         sb.append("ABC");
11         sb.append("软萌小鲨鱼");
12 
13 
14         //3.反转
15         sb.reverse();
16         System.out.println(sb);
17 
18         //获取长度
19         int lenth = sb.length();
20         System.out.println(lenth);
21 
22         //变回字符串
23         String str = sb.toString();
24         System.out.println(str);
25 
26 
27     }
28 }

1 public class demo12 {
2     public static void main(String[] args) {
3         StringBuilder sb = new StringBuilder();
4         sb.append("aaa").append("bbb").append("ccc");
5         System.out.println(sb);
6     }
7 }