开关盒中的变量范围 [英] Variable's scope in a switch case

问题描述

我想我不明白范围在切换情况下是如何工作的。

I think I don't understand how the scope works in a switch case.

有人可以向我解释为什么第一个代码不能编译而是第二个代码是吗？

Can someone explain to me why the first code doesn't compile but the second does ?

代码1：

 int key = 2;
 switch (key) {
 case 1:
      String str = "1";
      return str;
 case 2:
      String str = "2"; // duplicate declaration of "str" according to Eclipse.
      return str;
 }

代码2：

 int key = 2;
 if (key == 1) {
      String str = "1";
      return str;
 } else if (key == 2) {
      String str = "2";
      return str;
 }

为什么变量str的范围不包含在案例1中？

How come the scope of the variable "str" is not contained within Case 1 ?

如果我跳过案例1的声明，变量str永远不会被声明......

If I skip the declaration of case 1 the variable "str" is never declared...

推荐答案

我将重复其他人所说的内容：每个 case 子句中的变量范围对应于整个切换语句。但是，您可以使用大括号创建更多嵌套范围，如下所示：

I'll repeat what others have said: the scope of the variables in each case clause corresponds to the whole switch statement. You can, however, create further nested scopes with braces as follows:

int key = 2;
switch (key) {
case 1: {
    String str = "1";
    return str;
  }
case 2: {
    String str = "2";
    return str;
  }
}

生成的代码现在将成功编译，因为名为变量每个 case 子句中的 str 都在其自己的范围内。

The resulting code will now compile successfully since the variable named str in each case clause is in its own scope.

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