while循环中标记的continue语句

Question

The following simple examples cause compile-time error. But It's not clear why.

public static void main (String[] args) throws java.lang.Exception
{
    int i = 0;
    d:
    {
        System.out.println("d");
    }
    while(i < 10){

        i++;
        continue d;

    }
}

--and--

public static void main (String[] args) throws java.lang.Exception
{
    int i = 0;
    d:
    {
        System.out.println("d");
        while(i < 10){
            i++;
            continue d;
        }
    }
}

DEMO

But the following works fine:

public static void main (String[] args) throws java.lang.Exception
{
    int i = 0;
    d:
    while(i < 10){
        {
            System.out.println("d");
        }
        i++;
        continue d;

    }
}

Does it allow to tranfer control to the only while , for or do statement? It doesn't say in the JLS . What it actual says is:

A continue statement with label Identifier attempts to transfer control to the enclosing labeled statement (§14.7) that has the same Identifier as its label; that statement, which is called the continue target, then immediately ends the current iteration and begins a new one.

Answer 1

A continue means go to the start of a loop. So when you continue to a label, the label has to be on a loop. (It is not a goto statement ...)

---

Does it allow to tranfer control to the only while, for or do statement? It doesn't say in the JLS.

Actually, it does say.

Here's what JLS 14.6 (Java 8 revision) really says:

"A continue statement with label Identifier attempts to transfer control to the enclosing labeled statement (§14.7) that has the same Identifier as its label; that statement, which is called the continue target, then immediately ends the current iteration and begins a new one.

To be precise, a continue statement with label Identifier always completes abruptly, the reason being a continue with label Identifier.

The continue target must be a while, do, or for statement, or a compile-time error occurs. "

(Bolded in original!)

The bolded sentence says that the statement that the label is attached to (referred to as the "continue target") has to be a loop statement of some kind.

Answer 2

JLS 14.16

A continue statement may occur only in a while, do, or for statement (iteration statements) ;

The continue target must be a while, do, or for statement, or a compile-time error occurs.

---

A continue statement with label Identifier attempts to transfer control to the enclosing labeled statement (§14.7) that has the same Identifier as its label; that statement, which is called the continue target, then immediately ends the current iteration and begins a new one.

---

A continue statement must refer to a label within the immediately enclosing method, constructor, or initializer. There are no non-local jumps. If no labeled statement with Identifier as its label in the immediately enclosing method, constructor, or initializer contains the continue statement, a compile-time error occurs .