JavaSE-8.2【StringBuilder类】

 

 

package day8.learn_StringBuilder;

/*
3 StringBuilder类

3.1 StringBuilder类概述
    StringBuilder 是一个可变的字符串类，我们可以把它看成是一个容器，
    这里的可变指的是 StringBuilder 对象中的内容是可变的

3.2 StringBuilder类和String类的区别
    String类：内容是不可变的
    StringBuilder类：内容是可变的

3.3 StringBuilder类的常用构造方法
    public StringBuilder() 创建一个空白可变字符串对象，不含有任何内容
    public StringBuilder(String str) 根据字符串的内容，来创建可变字符串对象

3.4 StringBuilder类添加和反转方法
    public StringBuilder append(任意类型) 添加数据，并返回对象本身
    public StringBuilder reverse() 返回相反的字符序列

3.5 StringBuilder和String相互转换
    StringBuilder转换为String
        public String toString()：通过 toString() 就可以实现把 StringBuilder 转换为 String
    String转换为StringBuilder
        public StringBuilder(String s)：通过构造方法就可以实现把 String 转换为 StringBuilder

3.6 案例-字符串拼接升级版

3.7 案例-字符串反转升级版
 */

public class StringBuilderDemo {
    public static void main(String[] args) {
        test33();
        test34();
        test35();
        test36();
        test37();
    }

    public static void test33(){
        StringBuilder sb = new StringBuilder();
        System.out.println("sb:" + sb);
        System.out.println("sb.length:" + sb.length());

        StringBuilder sb2 = new StringBuilder("hello");
        System.out.println("sb2:" + sb2);
        System.out.println("sb2.length:" + sb2.length());
    }

    public static void test34(){
        StringBuilder sb = new StringBuilder();

        /*StringBuilder sb2 = sb.append("hello");
        System.out.println("sb:" + sb); //hello
        System.out.println("sb2:" + sb2); //hello
        System.out.println(sb == sb2); //true*/

        /*sb.append("山东");
        sb.append("菏泽");
        sb.append("曹县");
        sb.append("牛批");
        sb.append(666);
        System.out.println(sb);*/

        //链式编程
        sb.append("山东").append("菏泽").append("曹县").append("NB").append(666);
        System.out.println(sb);

        sb.reverse();
        System.out.println(sb);
    }

    public static void test35(){
        StringBuilder sb = new StringBuilder();
        sb.append("hello");

//        String s = sb; //error
        String s = sb.toString(); //ok
        System.out.println(s);

        String str = "java";
//        StringBuilder sb2 = str; //error
        StringBuilder sb2 = new StringBuilder(str); //ok
        System.out.println(sb2);
    }

    public static void test36(){
        int[] arr = {1, 2, 3, 4};
        String str = arr2Str(arr);
        System.out.println(str);
    }

    public static String arr2Str(int[] arr) {
        StringBuilder sb = new StringBuilder();
        sb.append("[");
        for(int i=0; i<arr.length; i++){
            if(i == arr.length-1){
                sb.append(arr[i]);
            }else {
                sb.append(arr[i]).append(", ");
            }
        }
        sb.append("]");

        String s = sb.toString();
        return s;
    }

    public static void test37(){
        String str = "happy";
        String result = reverseStr(str);
        System.out.println(result);
    }

    public static String reverseStr(String s){
        /*StringBuilder sb = new StringBuilder(s);
        sb.reverse();
        String ss = sb.toString();
        return ss;*/

        return new StringBuilder(s).reverse().toString(); //new StringBuilder()-->匿名对象
    }

}