scope

[sriranch]

Can any one explain why the following is not allowed in Java
int x; // outer scope
{
int x; // inner scope
}
One would assume that this should work.
Thanks
SRA

[Li Yang]

The outer scope variable x is accessible inside the inner scope, hence you have a name conflict when you define the inner variable x.

[Prasad Ballari]

sriranch,
Can u pls give me little more detailed code.coz,u can have a class variable and instance variable of same name but with different scope.
Prasad
------------------

[Jane Griscti]

Hi sriranch,
Well, it does work, to a point. It depends on the context. For example, it works fine in this code:

class TestScope {
    int x = 10;     // seen as an instance variable
    
    {
        int x = 5;  // as part of instance initializer
        System.out.println("Inner x: " + x);
    }
    
    public static void main(String[] args) {
        TestScope t = new TestScope();
        System.out.println("Outer x: " + t.x );
    }
}

However, it won't work in the following context:

    public void method() {
    
        int x = 20;
        
        {
          int x = 30;  // produces compile-error
        };
    }

The answer is in JLS §14.4.2

The name of a local variable v may not be redeclared as a local variable of the directly enclosing method, constructor or initializer block within the scope of v, or a compile-time
error occurs.

Hope that helps.
Jane

[Bob Kerfoot]

sriranch,
This probably will not help much but the JLS(Second Edition) simply states on page 281 that "if a declaration of an identifier as a local variable of the same method, constructor, or initializer block appears within the scope of a parameter or local variable of the same name, a compile-time error occurs".
Also, the only reason provided on page 282 is that "this restriction helps to detect some otherwise very obscure bugs".
Hope this helps.
Bob Kerfoot - SCJP