Java Class Constructors

Description

A constructor initializes an object during object creation when using new operator.

Java allows objects to initialize themselves when they are created. This automatic initialization is performed through the use of a constructor.

Syntax

It has the same name as the class. Constructors have no return type, not even void.

class ClassName{/*w w w.jav  a2 s .  co  m*/

   ClassName(parameter list){ // constructor
    ...
   }
}

Example

In the following code the Rectangle class in the following uses a constructor to set the dimensions:

 
class Rectangle {
  double width;/*  w  w w.ja  v a 2s  .  c  om*/
  double height;

  Rectangle() {
    width = 10;
    height = 10;
  }

  double area() {
    return width * height;
  }
}

public class Main {
  public static void main(String args[]) {
    Rectangle mybox1 = new Rectangle();
    double area;
    area = mybox1.area();
    System.out.println("Area is " + area);

  }
}

When this program is run, it generates the following results: