在Java中重新声明循环内部的变量 [英] Re-declaring variables inside loops in Java

问题描述

在Java中，我们不能在具有相同名称的另一个变量的同一范围内声明变量：

In Java, we cannot declare a variable in the same scope with the other variable which has the same name:

int someInteger = 3;

...

int someInteger = 13;

语法错误，无法编译。但是，如果我们把它放在一个循环中：

Syntax error, doesn't compile. However, if we put it inside a loop:

for (int i = 0; i < 10; i++) {
   int someInteger = 3;
}

生成错误，效果很好。我们基本上声明了相同的变量。是什么原因？我不明白/理解这背后的逻辑是什么？

Generates no error, works very well. We are basicly declaring the same variable. What is the reason? What is the logic that I don't know/understand behind this?

推荐答案

想想这样，在每次循环之后，范围被破坏，变量消失了。在下一个循环中，创建一个新的范围，并且可以在该范围内再次声明该变量。

Think of this way, after each loop, the scope is "destroyed", and the variable is gone. In the next loop, a new scope is created, and the variable can be declared again in that scope.

您也可以这样做，原因类似

You can also do this, for the similar reason

        {
           int someInteger = 3;
        }
        {
           int someInteger = 13;
        }

顺便说一下，Java不允许局部变量阴影，这可能不方便

By the way, Java does not allow local variable shadowing, which might be inconvenient

        int x = 3;
        {
           int x = 13; // error!
        }

        Consumer<Integer> consumer = (x)->print(x);  // ERROR! 
        // lambda parameter is treated like local variable

        Runnable r = ()->{ int x; ... } // ERROR
        // lambda body is treated like local block

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