Polymorphism(Compiletime vs Runtime),Method Overloading and Method Overriding in java.

Polymorphism.java

public class Polymorphism{

     public static void main(String []args){
         Base b1 = new Base();
         Derived d1 = new Derived();
         Base b2 = new Base();
         Derived d2 = new Derived();
         System.out.println("\n\n");
//Compiletime Polymorphism ->Method Overloading(i.e function overloading)
//(Methods have same name,diff parameters,inside same class)

//Runtime Polymorphism ->Method Overriding ->Dynamic Method Dispatch
//(Methods have same name,same parameters one in base class,other in derived class)
         /************************/
         Base b3 = new Derived();// UPCASTING
//Reference variable of parent class points(refers) to object of child class
         b3.func();  //same function present in both base and derived
         //But b3.func() calls the func() from derived class
         b3.func1();
         //Here b3.func2() gives error, can't find symbol
         System.out.println("\n\n");
//Derived d3 = new Base(); -> error "Base cannot be converted to Derived"
//The bank example at javatpoint is best to understand importance of upcasting
        /*********************/
         
     }
}

class Base 
{  int x;
   static int y;
 Base()
 {   x=x+1;y=y+1;
     System.out.println("Base Constructor "+x+" "+y); 
 }
 void func1()
 {
      System.out.println("Base Fuction");
 }
 void func()
 {
     System.out.println("Base Fuction with same name func");
 }
}

class Derived extends Base
{ 
Derived()//base constructor is called everytime derived constructor is called
{    x=x+1;y=y+1;
     System.out.println("Derived Constructor "+x+" "+y);
}
void func2()
{
     System.out.println("Derived Function");
}
void func()//method overriding
{
     System.out.println("Derived Fuction with same name func");
}
}
/*    OUTPUT
Base Constructor 1 1
Base Constructor 1 2
Derived Constructor 2 3
Base Constructor 1 4
Base Constructor 1 5
Derived Constructor 2 6



Base Constructor 1 7
Derived Constructor 2 8
Base Fuction
Derived Fuction with same name func

*/
/*
Inheritence:
https://www.geeksforgeeks.org/inheritance-in-java/
https://www.geeksforgeeks.org/gfact-52-java-object-creation-of-inherited-classes/
Polymorphism
https://www.javatpoint.com/runtime-polymorphism-in-java  (best resource)
*/