Scoping rules in Java

Question

Can someone help me understand the scoping rules in Java? This is clearly not valid:

    {
        int i = 0;
        System.out.println(i); // fine, of course
    }
    System.out.println(i); // syntax error

i is declared within the {}, and it's not available outside. So what about this:

    for (int i = 0; i < 10; i++) {
         System.out.println(i); // fine, of course
    }
    System.out.println(i);  // syntax error, same as above.

I'm surprised at the syntax error here. i is declared in the outer scope yet it is not available later on. Is it bound to the inner block scope by some special rule for for loops? Are there other scenarios where this can happen?

Answer 1

think of for loop actually represented like this:

{
  int i = 0;
  while (i < 10) {
    // your code
    i ++
  }
}

Answer 2

Is it bound to the inner block scope by some special rule for for loops?

Yes, this is exactly the case.

There's obviously the local variable declaration:

class Some { 
   public void x( int i ) { 
    System.out.println( i ); // valid 
   }
   int j = i; // not valid 
}

See also:

• Scope of a Declaration
• Scope of Local Variable Declarations

From the language specification.