Constructors In Java : Introduction

• Constructors in java are very special and have unique functionalities. We can initialize objects in Java as soon as they are created. This object initialization is performed by a special method called
• A constructor is a special method that initializes an object when they are created. Constructors in java are automatically invoked when objects are created.

Constructors In Java : Defining Rules

• Before defining constructors in java, we must know some rules. These are :
  • Constructor should have the same name as that of class name.
  • Constructor do not have any return type not even void.
• If you do not explicitly define a constructor for a class, then Java creates a default constructor for the class.

Constructors In Java : Types

• There are two Types of Constructors in Java that are used according to the need and logic. These are
  • Default Constructor
  • Parameterized Constructor
• Each of these constructors is explained below along with its syntax and a sample program.

1. Default Constructor

   • These constructors do not take any parameters.
     Syntax

     classname() { //body of default constructor }

      
   • An example could be :

   Cars() {               //body of default constructor             }

   
   
   • The default constructor if not specified is automatically created by Java.
   • Let’s modify the previous Area example using default constructor.
   
   
   Default Constructors : Example
   
   Default Constructors : Output
   
   

2. Parameterized Constructor

   • Those constructors which takes parameters for initializing object are called parameterized constructors.
   Syntax

   classname(parameter list…) {     }

    
   • An example could be : 

   Cars(int speed, int price) {             //body of parameterized constructor }

   
   
   • Let’s take the same example and add parameterized constructor in it.
   
   
   Parameterized Constructors : Example
   
   Parameterized Constructors : Output
   

Constructor Overloading : Introduction

• Constructor overloading means defining two or more constructors within the same class. In this case the constructors are said to be overloaded and the process is called constructor overloading.
• Now the question arises how Java determines which constructor to call . It is done by determining the type of arguments and the number of arguments in the constructor’s definition.
• Let us take an examples to show Constructor Overloading.


Constructor Overloading : Example

Constructor Overloading : Output