>> Polymorphism

Polymorphism

Method Overloading

Method Overriding

Constructor Overloading

Method overloading :

When  a class having more than one methods with same name but with different parameterization, is called method overloading. When the method or methods are called, java segregate/select the right method my its parameter.  The parameter could be : int , String, boolean, float , double  etc.

For example:

Create a class and create method with same name but with different parameters as below:

public class Employee {

      

       public void methodA()

       {

              System.out.println("This is methodA without parameter.");

       }

      

       public void methodA(int i)

       {

              System.out.println("This is methodA with parameter int i.");

       }

      

       public void methodA(String name , int i)

       {

              System.out.println("This is methodA with String and int parameters.");

       }

}

Let's call above method/s in below main method :

public class Run {

       public static void main(String[] args) {       

              Employee obj = new Employee();

              obj.methodA(); // This is method without parameter.

       }

}

Output:

This is methodA without parameter.

public class Run {

       public static void main(String[] args) {       

              Employee obj = new Employee();

              obj.methodA(5); // This is method with int parameter.

       }

}

Output:

This is methodA with parameter int i.

public class Run {

       public static void main(String[] args) {       

              Employee obj = new Employee();

              obj.methodA(); // This is method without parameter.

              obj.methodA(5); // This is method with int parameter.

              obj.methodA("Rose", 1); // This is method with String and int parameter.

       }

}

Output:

This is methodA without parameter.

This is methodA with parameter int i.

This is methodA with String and int parameters.

Method Overriding

When two or more classes having parent/child relationship, are having method with same name and same parameterization( or no parameterization), is called method overriding .  In such situation, when the method is called, the child method gets precedence.  

For example:

Parent class

public class Employee {

      

       public void methodA()

       {

              System.out.println("This is method in parent class.");

       }     

}

Child class

public class Dept extends Employee {

       public void methodA()

       {

              System.out.println("This is method in child class.");

       }

}

Running above codes:

public class Run {

       public static void main(String[] args) {       

              Dept obj = new Dept();

              obj.methodA();

       }

}

As you can see, both parent class and child class are having same method. In such situation, when we call the method , we get output from the child class as shown below:

Output:

This is method in child class.

Constructor Overloading

When you have a class with more than one constructors in it with different parameterizations , it is called constructor overloading . When you call the constructor, depending upon the parameter you pass, the respective constructor is called. The parameter could be : int , String, boolean, float , double  etc.

For example, below class is having three constructors with same name but different parameterization.  

public class Employee {

      

       Employee() {

              System.out.println("This is constructor without parameterization.");

       }

      

       Employee(int i) {

              System.out.println("This is constructor with int parameter.");

       }

      

       Employee(int i , String name) {

              System.out.println("This is constructor with int and String parameters.");

       }     

}

Let's call the constructors as below :

public class Run {

       public static void main(String[] args) {       

              Employee obj = new Employee();  //constructor without parameterization

       }

}

Output:

This is constructor without parameterization.

public class Run {

       public static void main(String[] args) {       

              Employee obj = new Employee(2, "Smith");  //constructor with int and String parameters.

       }

}

Output:

This is constructor with int and String parameters.

public class Run {

       public static void main(String[] args) {       

              Employee obj = new Employee(2, "Smith");  //constructor with int and String parameters.

              Employee obj1 = new Employee(10);  //constructor with int parameter.

              Employee obj2 = new Employee();  // constructor without parameterization.

       }

}

Output:

This is constructor with int and String parameters.

This is constructor with int parameter.

This is constructor without parameterization.