在Java中，break如何与嵌套循环交互？

Question

我知道一个break语句跳出一个循环，但它是跳出嵌套循环还是只是它当前的循环？

Answer 1

Without any adornment, break will just break out of the innermost loop. Thus in this code:

while (true) { // A
    while (true) { // B
         break;
    }
}

the break only exits loop B , so the code will loop forever.

However, Java has a feature called "named breaks" in which you can name your loops and then specify which one to break out of. For example:

A: while (true) {
    B: while (true) {
         break A;
    }
}

This code will not loop forever, because the break explicitly leaves loop A .

Fortunately, this same logic works for continue . By default, continue executes the next iteration of the innermost loop containing the continue statement, but it can also be used to jump to outer loop iterations as well by specifying a label of a loop to continue executing.

In languages other than Java, for example, C and C++, this "labeled break" statement does not exist and it's not easy to break out of a multiply nested loop. It can be done using the goto statement, though this is usually frowned upon. For example, here's what a nested break might look like in C, assuming you're willing to ignore Dijkstra's advice and use goto :

while (true) {
    while (true) {
        goto done;
    }
}
done:
   // Rest of the code here.

Hope this helps!

Answer 2

By default, it jumps out of the innermost loop. But you can specify labels and make it jump of outer loops too.

Answer 3

You can also break out by using Exceptions, so you can handle multiple reasons

 void fkt1() {
    try {
        while (true)
            fkt2();
    } catch (YourAbortException e) {
        e.printStackTrace();
    }

    //go on
}

void fkt2() {
    while (true)
        if (abort)
            throw new YourAbortException();
}

Answer 4

it breaks 1 loop . very simple. for ex:

for loop
   for loop
      break;
   end for loop
end for loop

break out of inner loop but still in outer loop