자바 코드에서 "loop :".

자바 코드에서 "loop :". 이것은 무엇이며 왜 컴파일됩니까?

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이 코드는 몇 분 동안 내 화면을 응시하도록 만들었습니다.

loop:
for (;;) {
    // ...
}

( 여기 137 행 )

나는 이것을 전에 본 적이 없으며 Java에 "루프"키워드가 있다는 것을 전혀 몰랐으며 (NetBeans는 키워드처럼 색상을 지정하지도 않음) JDK 6으로 잘 컴파일됩니다.

설명은 무엇입니까?

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그것은 아니다 keyword그것이이다 label.

용법:

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

문서 .

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다른 포스터가 말했듯이 키워드가 아니라 레이블입니다. 레이블을 사용하면 다음과 같은 작업을 수행 할 수 있습니다.

outer: for(;;) {
   inner: for(;;) {
     break outer;
   }
}

이것은 외부 루프를 끊을 수 있습니다.

문서 링크 .

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질문에 대한 답이 있지만 참고로 다음과 같습니다.

"이 Java 코드가 유효한 이유는 무엇입니까?"라는 인터뷰 질문에 대해 들어 본 적이 있습니다. (더 간단한 예를 제거했습니다. 여기에 더 비열한 것, Tim Büthe가 있습니다) :

url: http://www.myserver.com/myfile.mp3
downLoad(url);

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

Solution: two labels, url and http, a comment www.myserver.com/myfile.mp3 and 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).

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

outer:
for(;;){
    inner:
    for(;;){
        if(){
            break inner; // ends inner loop
        } else {
            break outer; // ends outer loop
        }
    }
}

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It's not a keyword; it's a label.

It allows you to go a labeled break and labeled continue.

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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:

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

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:

http://www.example.com/xyz.jsp
for (Foo foo1 : foolist)

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.

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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 line 148.

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You could write almost anything, as it is a label... You have an example here

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

int a = 0;
int b = 0
while (a<10){
    firstLoop:
    a++;
    while(true){
        b++
        if(b>10){
            break firstLoop;
        }
    }
 }

When b>10 the execution flow goes to the outer loop.

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It is a label, and labels in Java can be used with the break and continue key words for additional control over loops.

Here it is explained in a rather good way:

Thinking in Java, break and continue

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It is not a keyword, but a label. If inside the for loop you write break loop;, and you exit that loop.

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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.

참고URL : https://stackoverflow.com/questions/3821827/loop-in-java-code-what-is-this-and-why-does-it-compile