Sunday, December 19, 2010

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.

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