JavaSE-8.2【StringBuilder类】

 

 

  1 package day8.learn_StringBuilder;
  2 
  3 /*
  4 3 StringBuilder类
  5 
  6 3.1 StringBuilder类概述
  7     StringBuilder 是一个可变的字符串类，我们可以把它看成是一个容器，
  8     这里的可变指的是 StringBuilder 对象中的内容是可变的
  9 
 10 3.2 StringBuilder类和String类的区别
 11     String类：内容是不可变的
 12     StringBuilder类：内容是可变的
 13 
 14 3.3 StringBuilder类的常用构造方法
 15     public StringBuilder() 创建一个空白可变字符串对象，不含有任何内容
 16     public StringBuilder(String str) 根据字符串的内容，来创建可变字符串对象
 17 
 18 3.4 StringBuilder类添加和反转方法
 19     public StringBuilder append(任意类型) 添加数据，并返回对象本身
 20     public StringBuilder reverse() 返回相反的字符序列
 21 
 22 3.5 StringBuilder和String相互转换
 23     StringBuilder转换为String
 24         public String toString()：通过 toString() 就可以实现把 StringBuilder 转换为 String
 25     String转换为StringBuilder
 26         public StringBuilder(String s)：通过构造方法就可以实现把 String 转换为 StringBuilder
 27 
 28 3.6 案例-字符串拼接升级版
 29 
 30 3.7 案例-字符串反转升级版
 31  */
 32 
 33 public class StringBuilderDemo {
 34     public static void main(String[] args) {
 35         test33();
 36         test34();
 37         test35();
 38         test36();
 39         test37();
 40     }
 41 
 42     public static void test33(){
 43         StringBuilder sb = new StringBuilder();
 44         System.out.println("sb:" + sb);
 45         System.out.println("sb.length:" + sb.length());
 46 
 47         StringBuilder sb2 = new StringBuilder("hello");
 48         System.out.println("sb2:" + sb2);
 49         System.out.println("sb2.length:" + sb2.length());
 50     }
 51 
 52     public static void test34(){
 53         StringBuilder sb = new StringBuilder();
 54 
 55         /*StringBuilder sb2 = sb.append("hello");
 56         System.out.println("sb:" + sb); //hello
 57         System.out.println("sb2:" + sb2); //hello
 58         System.out.println(sb == sb2); //true*/
 59 
 60         /*sb.append("山东");
 61         sb.append("菏泽");
 62         sb.append("曹县");
 63         sb.append("牛批");
 64         sb.append(666);
 65         System.out.println(sb);*/
 66 
 67         //链式编程
 68         sb.append("山东").append("菏泽").append("曹县").append("NB").append(666);
 69         System.out.println(sb);
 70 
 71         sb.reverse();
 72         System.out.println(sb);
 73     }
 74 
 75     public static void test35(){
 76         StringBuilder sb = new StringBuilder();
 77         sb.append("hello");
 78 
 79 //        String s = sb; //error
 80         String s = sb.toString(); //ok
 81         System.out.println(s);
 82 
 83         String str = "java";
 84 //        StringBuilder sb2 = str; //error
 85         StringBuilder sb2 = new StringBuilder(str); //ok
 86         System.out.println(sb2);
 87     }
 88 
 89     public static void test36(){
 90         int[] arr = {1, 2, 3, 4};
 91         String str = arr2Str(arr);
 92         System.out.println(str);
 93     }
 94 
 95     public static String arr2Str(int[] arr) {
 96         StringBuilder sb = new StringBuilder();
 97         sb.append("[");
 98         for(int i=0; i<arr.length; i++){
 99             if(i == arr.length-1){
100                 sb.append(arr[i]);
101             }else {
102                 sb.append(arr[i]).append(", ");
103             }
104         }
105         sb.append("]");
106 
107         String s = sb.toString();
108         return s;
109     }
110 
111     public static void test37(){
112         String str = "happy";
113         String result = reverseStr(str);
114         System.out.println(result);
115     }
116 
117     public static String reverseStr(String s){
118         /*StringBuilder sb = new StringBuilder(s);
119         sb.reverse();
120         String ss = sb.toString();
121         return ss;*/
122 
123         return new StringBuilder(s).reverse().toString(); //new StringBuilder()-->匿名对象
124     }
125 
126 }

 

posted @ 2021-05-23 20:17  yub4by  阅读(61)  评论(0)    收藏  举报