Go4Expert

Go4Expert (http://www.go4expert.com/)
-   Java (http://www.go4expert.com/articles/java-tutorials/)
-   -   Constructors in Java (http://www.go4expert.com/articles/constructors-in-java-t4016/)

Sanskruti 25Apr2007 18:41

Constructors in Java
 
Every class has at least one it's own constructor. Constructor creates a instance for the class. Constructor initiates something related to the class's methods. Constructor is the method which name is same to the class. But there are many difference between the method s and the Constructor.In this example we will see that how to implement the constructor feature in a class. This program is using two classes. First class is TestConstructor and second is the main class which name is TestConstructorClient.

Code: Java

Class TestConstructor{
  int x,y;
  TestConstructor (int a, int b){
    x = a;
    y = b;
  }
  TestConstructor (){
     x = 2;
     y = 3;
  }
  int area(){
    int ar = x*y;
    return(ar);
  }
}
public class TestConstructorClient {
   public static void main(String[] args)
   {
     TestConstructor a = new TestConstructor ();
     System.out.println("Area of rectangle : " + a.area());
     TestConstructor b = new TestConstructor (1,1);
     System.out.println("Area of rectangle : " + b.area());
   }
}

Constructor Overloading



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.

Code: Java

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);
  }
}


mailtoabhishek88 3Aug2010 15:11

Re: Constructors in Java
 
why the default constructor is not provided by the compiler,if the class already have parameterized constructor ??

geracool7 3Oct2010 13:02

Re: Constructors in Java
 
hello i m sorabh doing btech final year and also doing java course from any private institute so i want to ask that how can i be perfect in java..any suggetion...

Healthcare 14Jun2012 09:58

Re: Constructors in Java
 
Nice description. The example is the better method to understand the concept.


All times are GMT +5.5. The time now is 09:09.