blocks|key|1131580|text|它不是keyword，它是label。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1131581|用法：|1131582|++++label1:
++++for+(;+;+)+{
++++++++label2:
++++++++for+(;+;+)+{
++++++++++++if+(condition1)+{
++++++++++++++++//+break+outer+loop
++++++++++++++++break+label1;
++++++++++++}
++++++++++++if+(condition2)+{
++++++++++++++++//+break+inner+loop
++++++++++++++++break+label2;
++++++++++++}
++++++++++++if+(condition3)+{
++++++++++++++++//+break+inner+loop
++++++++++++++++break;
++++++++++++}
++++++++}
++++}|code-block|syntax|javascript|1131583|Documentation。|1131584|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.7^0|3|7|D|5|0|0|0|0|D|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|13|8|@]|D|@$9|14|A|15|1|16]]|E|$]]|$1|O|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

It is not a <code>keyword</code> it is a <code>label</code>.

Usage: 

<pre><code> label1:
 for (; ; ) {
 label2:
 for (; ; ) {
 if (condition1) {
 // break outer loop
 break label1;
 }
 if (condition2) {
 // break inner loop
 break label2;
 }
 if (condition3) {
 // break inner loop
 break;
 }
 }
 }
</code></pre>

<a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.7" rel="noreferrer">Documentation</a>.

blocks|key|1131782|text|正如其他发帖者所说，它是一个标签，而不是一个关键词。通过使用标签，您可以执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1131783|outer:+for(;;)+{
+++inner:+for(;;)+{
+++++break+outer;
+++}
}|code-block|syntax|javascript|1131784|这允许中断外部循环。|1131785|Link+to+documentation。|offset|length|1131786|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.7^0|0|0|0|0|L|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@]|9|@$K|Y|L|Z|1|10]]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

As other posters have said, it is a label, not a keyword. Using labels allows you to do things like:

<pre><code>outer: for(;;) {
 inner: for(;;) {
 break outer;
 }
}
</code></pre>

This allows for breaking of the outer loop.

<a href="http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.7" rel="nofollow noreferrer">Link to documentation</a>.

blocks|key|917257|text|问题已经回答了，但作为附注：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|917258|我听说过一些面试问题，比如“为什么这段Java代码有效？”(去掉更简单的例子；下面是更糟糕的例子，thx+Tim+Büthe+)：|917259|url:+http://www.myserver.com/myfile.mp3
downLoad(url);|code-block|syntax|javascript|917260|你们都知道这段代码是什么吗(除了糟糕)？|917261|解决方案:两个标签，url和http，一个注释www.myserver.com/myfile.mp3和一个带有与标签同名的参数(url)的方法调用。是的，这是编译的(如果你在其他地方定义了方法调用和局部变量)。|offset|length|style|CODE|917262|entityMap^0|0|0|0|0|A|3|E|4|N|R|1S|3|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]|$M|Z|N|10|O|P]|$M|11|N|12|O|P]|$M|13|N|14|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|R|$]]

The question is answered, but as a side note:

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):

<pre class="lang-none prettyprint-override"><code>url: http://www.myserver.com/myfile.mp3
downLoad(url);
</code></pre>

Would you all know what this code is (apart from awful)?

Solution: two labels, <code>url</code> and <code>http</code>, a comment <code>www.myserver.com/myfile.mp3</code> and a method call with a parameter that has the same name (<code>url</code>) as the label. Yup, this compiles (if you define the method call and the local variable elsewhere).

blocks|key|1131891|text|这不是一个关键词，而是一个标签。它的目的是在嵌套循环中与break和continue关键字一起使用：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1131892|outer:
for(;;){
++++inner:
++++for(;;){
++++++++if(){
++++++++++++break+inner;+//+ends+inner+loop
++++++++}+else+{
++++++++++++break+outer;+//+ends+outer+loop
++++++++}
++++}
}|code-block|syntax|javascript|1131893|entityMap^0|S|5|Y|8|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

That's not a keyword, it's a label. It's meant to be used with the <code>break</code> and <code>continue</code> keywords inside nested loops:

<pre><code>outer:
for(;;){
 inner:
 for(;;){
 if(){
 break inner; // ends inner loop
 } else {
 break outer; // ends outer loop
 }
 }
}
</code></pre>

blocks|key|916894|text|它不是一个关键字；它是一个label。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|916895|它允许您使用标记的break和标记的continue。|style|CODE|916896|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/docs/books/jls/second_edition/html/statements.doc.html#78993^0|D|5|0|0|9|5|I|8|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@$A|U|B|V|F|G]|$A|W|B|X|F|G]]|9|@]|C|$]]|$1|H|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]]]

It's not a keyword; it's a <a href="http://java.sun.com/docs/books/jls/second_edition/html/statements.doc.html#78993" rel="nofollow noreferrer">label</a>.

It allows you to go a labeled <code>break</code> and labeled <code>continue</code>.

blocks|key|1131729|text|这是一个断点标签，允许您跳出指定的循环，而不仅仅是您恰好所在的最里面的循环。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1131730|它在line+148上使用。|offset|length|1131731|entityMap|0|LINK|mutability|MUTABLE|url|http://bazaar.launchpad.net/~play-developers/play/1.0/annotate/head:/framework/src/play/templates/TemplateCompiler.java#L148^0|0|2|8|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

It's a break point label, to allow you to break out of a specified loop, rather than simply the innermost one you happen to be in.

It's used on <a href="http://bazaar.launchpad.net/~play-developers/play/1.0/annotate/head:/framework/src/play/templates/TemplateCompiler.java#L148" rel="nofollow noreferrer">line 148</a>.

blocks|key|917359|text|这实际上是对seanizer对org.lif.java答案的评论的回复，但我想放入一些代码，这样我就不能使用评论功能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|917360|虽然我很少发现"break+label“的用法，但它确实偶尔会发生。最常见的情况是，当我在需要嵌套循环进行搜索的结构中搜索某些内容时，例如：|917361|search:
for+(State+state+:+stateList)
{
++for+(City+city+:+state.cityList)
++{
++++if+(city.zipcode.equals(wantZip))
++++{
++++++doSomethingTo(city);
++++++break+search;
++++}
++}
}|code-block|syntax|javascript|917362|通常在这种情况下，我会将整个对象放入一个子例程中，以便在命中时可以返回找到的对象，如果它落在循环的底部，我可以返回null来表示没有找到，或者可能会抛出异常。但这偶尔也是有用的。|917363|坦率地说，我认为Java的发明者之所以包含这个特性，是因为在这个特性和异常处理之间，他们消除了GOTO的最后两个合法用途。|917364|非常晚的附录：|917365|我曾经见过一大段很有趣的代码。程序员写道：|917366|http://www.example.com/xyz.jsp
for+(Foo+foo1+:+foolist)|917367|他实际上并没有说"example.com“，而是我们公司的网站。|917368|它给人的印象是代码中有一个URL。它编译成功，就像它做了一些事情一样。但是..。是干什么的呢？|917369|实际上，它什么也做不了。"http:“是一个他从未引用过的标签。然后，"//“使该行的其余部分成为注释。|917370|entityMap^0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|16|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|17|8|@]|9|@]|A|$G|H]]|$1|S|3|T|5|6|7|18|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|19|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

This is really a reply to seanizer's comment on org.life.java's answer, but I wanted to put in some code so I couldn't use the comment feature.

While it is very rare that I find a use for "break label", it does happen occassionally. The most common case is when I am searching for something that is in a structure requiring a nested loop to search, like:

<pre><code>search:
for (State state : stateList)
{
 for (City city : state.cityList)
 {
 if (city.zipcode.equals(wantZip))
 {
 doSomethingTo(city);
 break search;
 }
 }
}
</code></pre>

Usually in such cases I push the whole thing into a subroutine so that on a hit I can return the found object, and if it falls out the bottom of the loop I can return null to indicate a not found, or maybe throw an exception. But this is occasionally useful.

Frankly, I think the inventors of Java included this feature because between this and exception handling, they eliminated the last two legitimate uses for GOTO. 

Very late addendum:

I saw a great gag line of code once. The programmer wrote:

<pre><code>http://www.example.com/xyz.jsp
for (Foo foo1 : foolist)
</code></pre>

He didn't actually say "example.com" but our company's web site.

It gives the impression that there's a URL in the code. It compiles successfully, like it does something. But ... what does it do?

In reality it does nothing. "http:" is a label that he never references. Then the "//" makes the rest of the line a comment.

blocks|key|917088|text|这是一个标签，但请看下面的示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|917089|int+a+=+0;
int+b+=+0
while+(a<10){
++++firstLoop:
++++a%2B%2B;
++++while(true){
++++++++b%2B%2B
++++++++if(b>10){
++++++++++++break+firstLoop;
++++++++}
++++}
+}|code-block|syntax|javascript|917090|当为b>10时，执行流转到外部循环。|offset|length|style|CODE|917091|entityMap^0|0|0|2|4|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

It's a label, though look at the following example:

<pre><code>int a = 0;
int b = 0
while (a&lt;10){
 firstLoop:
 a++;
 while(true){
 b++
 if(b&gt;10){
 break firstLoop;
 }
 }
 }
</code></pre>

When <code>b&gt;10</code> the execution flow goes to the outer loop.

blocks|key|917193|text|你几乎可以写任何东西，因为它是一个标签。您有一个示例here|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|917194|entityMap|0|LINK|mutability|MUTABLE|url|http://geekycoder.wordpress.com/2008/06/25/tipjava-using-block-label-as-goto/^0|Q|4|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You could write almost anything, as it is a label...
You have an example <a href="http://geekycoder.wordpress.com/2008/06/25/tipjava-using-block-label-as-goto/" rel="nofollow">here</a>

blocks|key|1132157|text|这是一个标签。通常，Java中使用的标签用于在所需位置传输控制流，而所有关键字，如continue和break，都有指定的位置选择。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1132158|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It is a label. Generally a label used in Java to transfer the control flow at desired location while all keywords, like continue and break, have a specified choice of location.

This code just made me stare at my screen for a few minutes:

<pre><code>loop:
for (;;) {
 // ...
}
</code></pre>

(<a href="http://bazaar.launchpad.net/~play-developers/play/1.0/annotate/head:/framework/src/play/templates/TemplateCompiler.java#L137" rel="noreferrer">line 137 here</a>)

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.

What is the explanation?

"loop:" in Java code. What is this, and why does it compile?

Java

这段代码让我盯着屏幕看了几分钟：loop:for (;;) {    // ...}()我以前从未见过这种情况，我也不知道Java有一个“循环”关键字(NetBeans甚至不像关键字那样给它着色)，而且它在JDK6上编译得很好。解释是什么？

问Java代码中的"loop:“。这是什么，为什么要编译？
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问Java代码中的"loop:“。这是什么，为什么要编译？
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