To implement Java Program to demonstrate Method Overriding and Dynamic method dispatch

Explanation

This Java code demonstrates two fundamental object-oriented programming concepts: Method Overriding and Dynamic Method Dispatch (also known as Runtime Polymorphism).

1. Parent Class: We start with a base class named Parent. It has a single method, print(), which simply prints "Parent class" to the console.
2. Subclass1: subclass1 extends Parent. This means subclass1 inherits all members (methods and fields) of Parent. However, subclass1 also provides its own version of the print() method. This is Method Overriding – a subclass provides a specific implementation for a method that is already defined in its superclass. When subclass1's print() method is called, it will print "Subclass1".
3. Subclass2: Similar to subclass1, subclass2 also extends Parent and overrides the print() method. Its print() method prints "Subclass2".
4. Main Class: The Main class contains the main method, which is the entry point of the program.
   • Inside main, a variable a of type Parent is declared (Parent a;). This variable is a reference type that can point to objects of type Parent or any of its subclasses.
   • a = new subclass1();: Here, an object of subclass1 is created, and the reference a is made to point to this subclass1 object. This is a form of polymorphic assignment, where a superclass reference points to a subclass object.
   • a.print();: When print() is called using the a reference, the Java Virtual Machine (JVM) determines which print() method to execute at runtime. Since a is currently pointing to a subclass1 object, the print() method from subclass1 is invoked, printing "Subclass1". This decision made at runtime is Dynamic Method Dispatch.
   • a = new subclass2();: The reference a is now reassigned to point to a newly created subclass2 object.
   • a.print();: Again, print() is called. Because a now points to a subclass2 object, the JVM dynamically dispatches the call to the print() method of subclass2, printing "Subclass2".

In essence, the code demonstrates how a single reference variable (a of type Parent) can be used to invoke different implementations of the same method (print()) based on the actual type of the object it refers to at any given moment during program execution.

Algorithm

The program follows these steps in its main method:

1. Declare a reference variable a of type Parent.
2. Create an object of subclass1.
3. Assign the subclass1 object's reference to a.
4. Call the print() method using the a reference. The JVM dynamically determines and executes subclass1's print() method.
5. Create an object of subclass2.
6. Assign the subclass2 object's reference to a (overwriting the previous reference).
7. Call the print() method using the a reference. The JVM dynamically determines and executes subclass2's print() method.