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

问题描述

在Java中，我们不能声明一个变量与另一个同名变量在同一范围内:

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;
}

不会产生错误，效果很好.我们基本上是在声明相同的变量.是什么原因?我不知道/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

这样想，每次循环后，作用域就销毁"了，变量就没了.在下一个循环中，会创建一个新的作用域，并且可以在该作用域中再次声明该变量.

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.

出于类似的原因，您也可以这样做

You can also do this, for the similar reason

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

顺便说一句，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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