java – while循环中标记的continue语句

以下简单示例会导致编译时错误.但目前尚不清楚为什么.

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

        i++;
        continue d;

    }
}

– 和 –

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

但以下工作正常：

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

    }
}

它是否允许将控制转移到while,for或do语句？它没有在JLS中说.实际上说的是：

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.

解决方法

继续意味着转到循环的开始.因此,当您继续使用标签时,标签必须处于循环状态. (这不是goto声明……)

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

实际上,确实如此.

这是JLS 14.6(Java 8修订版)真正说的：

“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.“

(用原文加粗！)

粗体句子说标签所附的声明(称为“继续目标”)必须是某种循环声明.