Block scope variables

This will compile

class X
{  
    public static void main(String args[])
    {
        {
            int a = 2;
        }
        {
            int a = 3;
        }       
    }
}

This won't

class X
{  
    public static void main(String args[])
    {

        int a = 2;

        {
            int a = 3;
        }       
    }
}

I expected both to compile (maybe it is the way C works?). What is the reason because it is not possible to declare a variable in a block with the same name of one in the outer block?