在没有“循环”的java中使用标签 [英] using labels in java without "loops"

问题描述

我一直以为标签必须只用于循环，但似乎没有。给出这样的代码：

I always thought that the labels must be used only with loops but it seems not. Giving such code:

public class LabelTest {
    public static void main(String[] args) {
        label1: System.out.println("");
        label2: LabelTest t = new LabelTest();  
    }                                               
}

当标记为label1的编译行编译但代码在label2给出错误。为什么？为什么我要标记不是循环的语句？

When compiled line labeled "label1" compiles but the code at "label2" gives errors. Why's that? And why would I want to label statements which are not "loops"?

推荐答案

由于无法应用标签而出现错误变量声明，这就是如何定义语言语法（a label只能在 Statement 之前，而 LocalVariableDeclarationStatement 不是 Statement ）。原因可能是它可能导致关于变量范围的混淆。这有效：

You get an error because a label cannot be applied to variable declarations, that's just how the language grammar is defined (a label can only precede a Statement, and a LocalVariableDeclarationStatement is not a Statement). The reason is probably that it could cause confusion concerning variable scope. This works:

    label1: System.out.println("");
    label2: { LabelTest t = new LabelTest(); }

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