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scattered

  • Blocks
    • anonymous inner class is for overriding methods of super class.
    • static blocks are called just once "say at class loading time".
    • anonymous blocks are called every time a constructor is called but before it.
static{ // block executed at class load time just once }
{ //anonymous block within class scope called before each instantiation call }
  • Enumeration is an interface that provide an abstract mechanism for visiting elements.
    • enum Meal{
    BREAKFAST(7,30),LUNCH(1,30);
    private int h,m;
    Meal(int h, int m){
    this.h=h;this.m=m}....
  • Polymorphism is that you declare, say, a method argument of a particular type and at run-time be able to have that argument refer to any sub-type. 
    • void methodName( ArrayList <Animal>  list ){
    list.add( new Dog() ) }
    what if i passed a cat list, i'll then end up having a dog in my cat list, so since at run-time JVM knows the type of arrays, but not the type of collection.
    • < ? extends  > can't add to the collection
    • < ? super  > to enable adding ( adding higher in inheritance ) 

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