chapter 2 Object orienation polymorphism

[Mohit G Gupta]

SCJP1.6 JAVA 6 CERTIFICATION Guide-310-065
by Katherine Sierra (Author), Bert Bates (Author)


chapter 2:object orienation
pg-102

even though the compiler
only knows about the declared reference type, the Java Virtual Machine (JVM)
at runtime knows what the object really is. And that means that even if the
PlayerPiece object's displayShape() method is called using a GameShape
reference variable, if the PlayerPiece overrides the displayShape() method, the
JVM will invoke the PlayerPiece version! The JVM looks at the real object at the
other end of the reference, "sees" that it has overridden the method of the declared
reference variable type, and invokes the method of the object's actual class


can anyone illustrate with an example

[Prasad Kharkar]

well you will get all this in the next part of the book in the Overriding and overloading section
this is the example I have tried in the book hope this helps

   /*  A Program to demonstrate the difference between Overriding and Overloading
	Developer: Prasad Kharkar
*/
class Animal
{
	public void eat()	// original method
	{
		System.out.println("Animal"); 
	} // End of Method
}//End of class

public class Horse extends Animal
{
	public void eat()	// overriding the method in Animal class
	{
		System.out.println("Horse");
	}// End of method
	
	public void eat(String s)	// overloads the eat method in Animal
	{
		
		System.out.println("String");
	} // End of overloaded method

public static void main(String args[])
	{
		Animal a = new Animal();
		Horse h1 = new Horse();
		Animal ah = new Horse();	// object of Horse but reference of Animal class
		Horse h2 = new Horse();
		Animal a2 = new Animal();
		a.eat();				//prints Animal
		h1.eat();				//prints Horse
		ah.eat();				//prints Horse 
		h2.eat("A");			//prints String
	//	a2.eat("A"); // This was commented because the compiler throws an error that animal class cannot access the methods of horse class
	}
}

 

Happy preparation