“循环：”在 Java 代码中。这是什么，为什么要编译？
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"loop:" in Java code. What is this, and why does it compile?
提问by Amy B
This code just made me stare at my screen for a few minutes:
这段代码让我盯着屏幕看了几分钟：
loop:
for (;;) {
// ...
}
I have never seen this before, and I had no idea Java has a "loop" keyword (NetBeans doesn't even color it like a keyword), and it does compile fine with JDK 6.
我以前从未见过这个，我不知道 Java 有一个“循环”关键字（NetBeans 甚至不会像关键字那样给它上色），而且它在 JDK 6 中编译得很好。
What is the explanation?
解释是什么？
采纳答案by Jigar Joshi
It is not a keywordit is a label.
它不是一个keyword它是一个label。
Usage:
用法：
label1:
for (; ; ) {
label2:
for (; ; ) {
if (condition1) {
// break outer loop
break label1;
}
if (condition2) {
// break inner loop
break label2;
}
if (condition3) {
// break inner loop
break;
}
}
}
文档。
回答by codaddict
回答by PaulJWilliams
回答by vstoyanov
It is a label, and labels in Java can be used with the breakand continuekey words for additional control over loops.
它是一个标签，Java 中的标签可以与break和continue关键字一起使用，以对循环进行额外控制。
Here it is explained in a rather good way:
这里以一种相当好的方式解释了它：
回答by Rob Di Marco
As other posters have said, it is a label, not a keyword. Using labels allows you to do things like:
正如其他海报所说，它是一个标签，而不是一个关键词。使用标签可以执行以下操作：
outer: for(;;) {
inner: for(;;) {
break outer;
}
}
This allows for breaking of the outer loop.
这允许断开外环。
回答by Alberto Zaccagni
It's a label, though look at the following example:
这是一个标签，但请看以下示例：
int a = 0;
int b = 0
while (a<10){
firstLoop:
a++;
while(true){
b++
if(b>10){
break firstLoop;
}
}
}
When b>10the execution flow goes to the outer loop.
当b>10执行流程转到外循环时。
回答by Michael Borgwardt
That's not a keyword, it's a label. It's meant to be used with the breakand continuekeywords inside nested loops:
这不是关键字，而是标签。它旨在与嵌套循环内的breakandcontinue关键字一起使用：
outer:
for(;;){
inner:
for(;;){
if(){
break inner; // ends inner loop
} else {
break outer; // ends outer loop
}
}
}
回答by SoulWanderer
回答by greuze
It is not a keyword, but a label. If inside the forloop you write break loop;, and you exit that loop.
它不是关键字，而是标签。如果在for循环中你写了break loop;，你就退出循环。
回答by Sean Patrick Floyd
The question is answered, but as a side note:
这个问题得到了回答，但作为旁注：
I have heard of interview questions a la "Why is this Java code valid?" (stripped the simpler example; here's the meaner one, thx Tim Büthe):
我听说过“为什么这个 Java 代码有效？”这样的面试问题。（去掉了更简单的例子；这是更简单的例子，感谢 Tim Büthe）：
url: http://www.myserver.com/myfile.mp3
downLoad(url);
Would you all know what this code is (apart from awful)?
你们都知道这个代码是什么（除了可怕的）？
Solution: two labels, urland http, a comment www.myserver.com/myfile.mp3and a method call with a parameter that has the same name (url) as the label. Yup, this compiles (if you define the method call and the local variable elsewhere).
解决方案：两个标签，url和http，一个注释www.myserver.com/myfile.mp3和一个方法调用，参数url与标签同名 ( )。是的，这会编译（如果您在其他地方定义方法调用和局部变量）。
