你不能比较字符串连接和字符串。格式由上面的程序。

你也可以尝试交换使用你的字符串的位置。格式和连接在你的代码块如下所示

public static void main(String[] args) throws Exception {      
  long start = System.currentTimeMillis();

  for( int i=0;i<1000000; i++){
    String s = String.format( "Hi %s; Hi to you %s",i, + i*2);
  }

  long end = System.currentTimeMillis();
  System.out.println("Format = " + ((end - start)) + " millisecond");
  start = System.currentTimeMillis();

  for( int i=0;i<1000000; i++){
    String s = "Hi " + i + "; Hi to you " + i*2;
  }

  end = System.currentTimeMillis();
  System.out.println("Concatenation = " + ((end - start)) + " millisecond") ;
}

您会惊讶地发现，Format在这里工作得更快。这是因为创建的初始对象可能不会被释放，内存分配可能会出现问题，从而影响性能。

错误的测试重复多次 不应该使用{}%s。

public static void main(String[] args) throws Exception {
long start = System.currentTimeMillis();
for (int i = 0; i < 1000000; i++) {
  String s = "Hi " + i + "; Hi to you " + i * 2;
}
long end = System.currentTimeMillis();
System.out.println("Concatenation = " + ((end - start)) + " millisecond");

start = System.currentTimeMillis();
for (int i = 0; i < 1000000; i++) {
  String s = String.format("Hi %s; Hi to you %s", i, +i * 2);
}
end = System.currentTimeMillis();
System.out.println("Wrong use of the message format  = " + ((end - start)) + " millisecond");

start = System.currentTimeMillis();
for (int i = 0; i < 1000000; i++) {
  String s = String.format("Hi {0}; Hi to you {1}", i, +i * 2);
}
end = System.currentTimeMillis();
System.out.println("Good use of the message format = " + ((end - start)) + " millisecond");

}

Concatenation = 88 millisecond
Wrong use of the message format  = 1075 millisecond 
Good use of the message format = 376 millisecond

我建议使用String.format()是更好的实践。主要原因是String.format()可以更容易地使用从资源文件加载的文本进行本地化，而拼接如果不为每种语言生成带有不同代码的新可执行文件就无法进行本地化。

如果你打算让你的应用程序本地化，你也应该养成为你的格式标记指定参数位置的习惯:

"Hello %1$s the time is %2$t"

然后可以对其进行本地化，并交换名称和时间令牌，而不需要重新编译可执行文件以考虑不同的顺序。对于参数位置，你也可以重复使用相同的参数，而不需要将其传递给函数两次:

String.format("Hello %1$s, your name is %1$s and the time is %2$t", name, time)

哪一个更容易读，取决于你的大脑如何工作。

你已经得到答案了。

这是个人喜好的问题。

我认为，字符串连接稍微快一些，但这应该可以忽略不计。

性能:

public static void main(String[] args) throws Exception {      
  long start = System.currentTimeMillis();
  for(int i = 0; i < 1000000; i++){
    String s = "Hi " + i + "; Hi to you " + i*2;
  }
  long end = System.currentTimeMillis();
  System.out.println("Concatenation = " + ((end - start)) + " millisecond") ;

  start = System.currentTimeMillis();
  for(int i = 0; i < 1000000; i++){
    String s = String.format("Hi %s; Hi to you %s",i, + i*2);
  }
  end = System.currentTimeMillis();
  System.out.println("Format = " + ((end - start)) + " millisecond");
}

授时结果如下:

串联= 265毫秒 格式= 4141毫秒

因此，连接比String.format快得多。

It takes a little time to get used to String.Format, but it's worth it in most cases. In the world of NRA (never repeat anything) it's extremely useful to keep your tokenized messages (logging or user) in a Constant library (I prefer what amounts to a static class) and call them as necessary with String.Format regardless of whether you are localizing or not. Trying to use such a library with a concatenation method is harder to read, troubleshoot, proofread, and manage with any any approach that requires concatenation. Replacement is an option, but I doubt it's performant. After years of use, my biggest problem with String.Format is the length of the call is inconveniently long when I'm passing it into another function (like Msg), but that's easy to get around with a custom function to serve as an alias.