Java Constructor Example - Constructor Overloading in Java

Constructor Overloading in Java

Here, you will learn more about Constructor and how constructors are overloaded in Java. This section provides you a brief introduction about the Constructor that are overloaded in the given program with complete code absolutely in running state i.e. provided for best illustration about the constructor overloading in Java.

Constructors are used to assign initial values to instance variables of the class. A default constructor with no arguments will be called automatically by the Java Virtual Machine (JVM). Constructor is always called by new operator. Constructor are declared just like as we declare methods, except that the constructor don't have any return type. Constructor can be overloaded provided they should have different arguments because JVM differentiates constructors on the basis of arguments passed in the constructor.

Whenever we assign the name of the method same as class name. Remember this method should not have any return type. This is called as constructor overloading.

We have made one program on a constructor overloading, after going through it the concept of constructor overloading will get more clear. In the example below we have made three overloaded constructors each having different arguments types so that the JVM can differentiates between the various constructors.

The code of the program is given below:


public class ConstructorOverloading{

  public static void main(String args[]){

    Rectangle rectangle1=new Rectangle(2,4);

    int areaInFirstConstructor=rectangle1.first();

    System.out.println(" The area of a rectangle in 

  first constructor is :  " + areaInFirstConstructor);

    Rectangle rectangle2=new Rectangle(5);

    int areaInSecondConstructor=rectangle2.second();

    System.out.println(" The area of a rectangle in 

   first constructor is :  " + areaInSecondConstructor);

    Rectangle rectangle3=new Rectangle(2.0f);

    float areaInThirdConstructor=rectangle3.third();

    System.out.println(" The area of a rectangle in first 

        constructor is :  " + areaInThirdConstructor);

    Rectangle rectangle4=new Rectangle(3.0f,2.0f);

    float areaInFourthConstructor=rectangle4.fourth();

    System.out.println(" The area of a rectangle in first 

      constructor is :  " + areaInFourthConstructor);

  }

}



class Rectangle{

  int l, b;

  float p, q;

  public Rectangle(int x, int y){

    l = x;

    b = y;

  }

  public int first(){ 

    return(l * b);

  }

  public Rectangle(int x){

    l = x;

    b = x;

  }

  public int second(){

    return(l * b);

  }

  public Rectangle(float x){

    p = x;

    q = x;

  }

  public float third(){

    return(p * q);

  }

  public Rectangle(float x, float y){

    p = x;

    q = y;

  }

  public float fourth(){

    return(p * q);

  }

}

Output of the program is given below:

C:\java>java ConstructorOverloading
The area of a rectangle in first constructor is : 8
The area of a rectangle in first constructor is : 25
The area of a rectangle in first constructor is : 4.0
The area of a rectangle in first constructor is : 6.0