11.StringBuilder的使用

package com.itheima.stringbuilder;

public class Demo1StringBuilDer {
    public static void main(String[] args) {
        long start=System.currentTimeMillis();
       StringBuilder sb=new StringBuilder();
        for (int i = 1; i <=5000000 ; i++) {
            sb.append(i);
        }
        System.out.println(sb);
        long end=System.currentTimeMillis();
        System.out.println(end-start);
    }

    private static void method() {
        long start=System.currentTimeMillis();
        System.out.println(start);
        String s="";
        for (int i = 1; i <=50000 ; i++) {
            s+=i;
        }
        System.out.println(s);
        long end=System.currentTimeMillis();
        System.out.println(end-start);
    }
}

package com.itheima.stringbuilder;

public class Demo2StringBuilder {
    public static void main(String[] args) {
        StringBuilder sb=new StringBuilder();
        System.out.println(sb);
        StringBuilder sb2=new StringBuilder("abc");
        System.out.println(sb2);
        sb.append(123);
        sb.append("abc");
        sb.append(true);
        System.out.println(sb);
        StringBuilder sb3=sb.append(true);
        System.out.println(sb3);
        sb.append("红色").append("蓝色").append("绿色");
        System.out.println(sb);
        sb.reverse();
        System.out.println("反转:"+sb );
        System.out.println("sb中字符的个数为："+sb.length());
        String s=sb.toString();
        System.out.println(s);


    }
}

package com.itheima.stringbuilder;

import java.util.Scanner;

public class DemoStringBuilderRevert {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        System.out.println("请输入对称字符串：");
        String s=sc.nextLine();
        StringBuilder sb=new StringBuilder(s);
        sb.reverse();
        if (s.equals(sb.toString())){
            System.out.println("是对称字符串");
        }else {
            System.out.println("不是对称字符串");
        }

        int[] arr ={1,2,3};
        String s1 = arrayToString(arr);
        System.out.println(s1);
    }
    public static String arrayToString(int[] arr){
        StringBuilder sb=new StringBuilder("[");
        for (int i = 0; i < arr.length; i++) {
            if (i==arr.length-1){
                sb.append(arr[i]).append("]");
            }else {
                sb.append(arr[i]).append(",");
            }
        }
        return sb.toString();
    }
}