Java & C#_Object Oriented Programing3

Polymorphism:

• If one task is performed in different ways it is known as polymorphism.
• In Java, we use method overloading and method overriding to achieve polymorphism.
• Example:
• Normal methods: student1(), student2(), student3(), … and so no.
• In Polymorphism: student(), student(), student(), … and so no. (Same names)

Method Overloading:

            If a class has multiple methods (or Constructors) with the same name but different parameters, it is known as method overloading.

            Way to achieve method overloading:

1. By changing the number of arguments
2. By changing the data type.

• Example Program:

public class Overloading {     void add(int a, int b)     {         System.out.println(a+b);     }     void add(double a, double b)     {         System.out.println(a+b);     }     void add(int a, int b, int c)     {         System.out.println(a+b+c);     }     public static void main(String[] args)     {         Overloading ol = new Overloading();         ol.add(1, 3);         ol.add(2.3, 3.1);         ol.add(1, 2, 3);     } }

  

Method Overriding:

                    If the subclass (child class) has the same method as declared in the parent class, it is known as method overriding.

                Rules for method overriding:

1. The method must have the same name as in the parent class.
2. The method must have the same parameter as in the parent class.
3. Must be an IS-A relationship (Inheritance).

            Uses of method overriding:

1. It is used to provide specific implementation of a method already provided by its super class (parent class).

 

public class OverridingParent {     int num1 = 10;     public void addition()     {         int num2 = 20;         int res = num1+num2;         System.out.println(res);     } }

public class OverridingChild extends OverridingParent {     int num1 = 20;     public void addition()     {         int num2 = 30;         int num3 = 40;         int res = num1+num2+num3;         System.out.println(res);     }     public static void main(String args[])     {         OverridingChild oc = new OverridingChild();         oc.addition();     } }

Super Keyword:

            The ‘super’ keyword is a reference variable that is used to refer to the immediate parent class object. Or the ‘super’ keyword is used in subclasses to access the superclass method.

Usage of the ‘super’ keyword:

1. To refer immediate parent class instance variable.
2. To invoke the immediate parent class method.
3. To invoke immediate parent class constructor.

    Example Program:

public class SuperParentClass {     String name = "Parent";     public void display()     {         System.out.println(name);     } }

public class SuperChildClass extends SuperParentClass {     String name = "child";     public void display()     {         System.out.println(name);         System.out.println(super.name);     }     public void show()     {         super.display();     }     public static void main(String args[])     {         SuperChildClass sc = new SuperChildClass();         System.out.println("****************");         sc.display();         System.out.println("****************");         sc.show();     } }

Final Keyword:

• The ‘final’ keyword is a non-access modifier application only to a variable, a method, or a class.
• The final keyword is used to denote Constants.
• Final Variable: To create constant variables.
• Final Method: To prevent method overriding.
• Final Class: To prevent Inheritance.

    Example: In an Id Card the id card number is always final, the name and remaining details we can change.

    Example Program:

public class FinalKey {     public static void main(String[] args) {         int a = 10;         final int b = 20;         a = 20;         //Error: because b is final         b = 40;     } }

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