Java- Variable Declaration

December 19, 2010 2-minute read

java

                      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
```
  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.