Java- Variable Declaration

                      Variable Declaration
                              |
x---------------------------- x------------------------------ x
|                             |                               |
Local                    Class-level                   Super class-level
|                             |                               |
local to a function     instance variables            instance variables
                        static variables              static variables
                        private variables

 Private variables
  |
  x-- direct reference

 Instance variables
  |
  x-- direct reference
  |
  x-- instance reference 

 
 Static variables
  |
  x-- direct reference
  |
  x-- instance reference (conventionally discouraged)
  |
  x-- static reference

Note: Static variable declaration in the main() causes compilation error : illegal start of expression.
* Local variable should not be static

* The keywords that can come with an Outer class        –       abstract
                                                                final
                                                                public
* The keywords that can come with a Nested class        -       static
                                                                private
                                                                protected
                                                                public 

* The only modifier that can come with a local variable is final.

* Non-static nested class = Inner class

class VarDeclaration {
 public static void main(String[] args) {
 static int i=0;
  OtherClass oc = new OtherClass();
  oc.showX();
 }
}

class SomeClass {
 int x = 10;//super class-level
}

class OtherClass extends SomeClass {
 int x = 20;//class-level
 void showX() {
  int x = 30;//local
  System.out.println("local x: " + x);
  System.out.println("class-level x: " + 
   this.x);
  System.out.println("super class-level x: " + 
   super.x);
 }
}
* Predefined reference variable refines the scope of the variables with same name declared in different levels.
* Predefined reference should not be done in static context.