“Undefined label” error in java when using labeled break

问题

I'm trying to analyse a java code and see what it does, but in the "break label" line it gives the "Undefined label" error. from my understanding java unlike c# allows breaking into a scope outside of the current scope. isn't that right?

if (conditions) {
  // some code
  if (conditions) {
    break label;
  }
  // some code
}

for (;;) {
  if (conditions) {
    // some code
  }
  // some code
  break;
  label: 
  // some code
}

回答1:

In your example, you are trying to use break label; as though it were similar to the goto label; syntax in C/C++. This is not how it works in Java.

in Java, the break label; syntax is applicable only when you are using nested loops and you need to break out from an inner loop to one of the outer loops in question.

For example:

outer: while(some condition) {
    inner: while(another condition) {
        innermost: while(yet another condition) {
            if(breaking_condition) {
                break inner;
            } else if (one more breaking condition) {
                break outer;
            }
        }
    }
}

Refer this tutorial from Oracle:

https://docs.oracle.com/javase/tutorial/java/nutsandbolts/branch.html

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Hope this helps!

来源：https://stackoverflow.com/questions/44129866/undefined-label-error-in-java-when-using-labeled-break