Re-declaring variables inside loops in Java

Question

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;

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

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

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?

Answer 1

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.

You can also do this, for the similar reason

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

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