JAvaの5種類の文字列のつなぎ合わせの方法と性能の紹介

package com.example.sunny.practice_213;

public class CutString {

    //    
    public String testPlus() {
       String s = "";
       for (int i = 0; i < 10000; i++) {
           s = s + String.valueOf(i);
       }
       return s;
    }

    //  
    public String testConcat() {
       String s = "";
       for (int i = 0; i < 10000; i++) {
           s = s.concat(String.valueOf(i));
       }
       return s;
    }

    //   testStringBuffer    ，    
    public String testJoin() {
       String[] list = new String[10000];
       for (int i = 0; i < 10000; i++) {
           list[i] = String.valueOf(i);
       }
       return StringUtils.join(list, "");
    }

    public String testStringBuffer() {
       StringBuffer sb = new StringBuffer();
       long l1 = System.currentTimeMillis();
       for (int i = 0; i < 10000; i++){
           sb.append(String.valueOf(i));
       }
       long l2 = System.currentTimeMillis();
       System.out.println(l2 - l1);
       return sb.toString();

    }

    //       
    public void testStringBuilder() {
       StringBuilder sb = new StringBuilder();
       for (int i = 0; i < 100000; i++) {
           sb.append(String.valueOf(i));
       }
       sb.toString();
    }

    public static void main(String[] args) {
       System.out.println(new CutString().testStringBuffer());
    }
}