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。