JAVA字符串拼接速度对比

String + 与 StringBuilder 速度

    SimpleDateFormat formatter = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss:SSS");
String string = "";
StringBuilder stringBuilder = new StringBuilder();
System.out.println("time before string+string "+formatter.format(new Date()));
for (int i = 0; i < 1000000; i++) {
	string = string + "1";
}
System.out.println("time after string+string "+formatter.format(new Date()));
System.out.println("time before stringBuilder.append "+formatter.format(new Date()));
for (int i = 0; i < 1000000; i++) {
	stringBuilder.append("1");
}
System.out.println("time after stringBuilder.append "+formatter.format(new Date()));

试验结果：前者需要5分多钟，后者是毫秒级的。只知道速度有差异，没想到会差这么多，被惊到了！

time before string+string 29-五月-2018 22:33:35:347
time after string+string 29-五月-2018 22:38:53:943
time before stringBuilder.append 29-五月-2018 22:38:53:944
time after stringBuilder.append 29-五月-2018 22:38:53:955

注意，StringBuilder不是线程安全的（StringBuffer：线程安全）