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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