Java字符串拼接效率测试过程解析

测试代码：

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;
  }
}

测试结果：

结论：

　　在少量字符串拼接时还看不出差别，但随着数量的增加，String+拼接效率显著降低。在达到100万次，我本机电脑已经无法执行String+拼接了，StringBuilder效率略高于StringBuffer。所以在开发过程中通常情况下推荐使用StringBuilder。

　　StringBuffer和StringBuilder的区别在于StringBuffer是线程安全的。

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