Java字符串拼接效率测试过程解析

public class StringJoinTest {
  public static void main(String[] args) {
    int count = 10000;
    long begin, end, time;
    begin = System.currentTimeMillis();
    testString(count);
    end = System.currentTimeMillis();
    time = end - begin;
    System.out.println("拼接" + count + "次，String消耗时间：" + time + "毫秒");

    begin = System.currentTimeMillis();
    testStringBuffer(count);
    end = System.currentTimeMillis();
    time = end - begin;
    System.out.println("拼接" + count + "次，StringBuffer消耗时间：" + time + "毫秒");

    begin = System.currentTimeMillis();
    testStringBuilder(count);
    end = System.currentTimeMillis();
    time = end - begin;
    System.out.println("拼接" + count + "次，StringBuilder消耗时间：" + time + "毫秒");
  }

  private static String testStringBuilder(int count) {
    StringBuilder tem = new StringBuilder();
    for (int i = 0; i < count; i++) {
      tem.append("hello world!");
    }
    return tem.toString();
  }

  private static String testStringBuffer(int count) {
    StringBuffer tem = new StringBuffer();
    for (int i = 0; i < count; i++) {
      tem.append("hello world!");
    }
    return tem.toString();
  }

  private static String testString(int count) {
    String tem = "";
    for (int i = 0; i < count; i++) {
      tem += "hello world!";
    }
    return tem;
  }
}