Constructor function

A Constructor function, in computer programming, is a member function of a class and always has the same name as the class.

It is used to create an object instance of a particular class and possibly also populate some or all of that object instance's attributes.

A class may have more than one constructor function allowing multiple ways to create an object instance, as in example 2 below, an account can be created without supplying an initial balance and one where an initial balance can be supplied in the call to the constructor function.

Example 1. (In Javascript)

// constructor function
function MyObject(attributeA, attributeB) {
  this.attributeA = attributeA
  this.attributeB = attributeB
}

// create an Object
obj = new MyObject('red', 1000)

Example 2. (In Java)

public class Account {

       protected double balance;

       // Constructor function        
       public Account( )

{

              balance = 0.0;

}

       // Constructor function to initialize balance
       public Account( double amount )

{ balance = amount; }

       public double getbalance()

{

               return balance;

} }

public class AccountTester {

       public static void main( String args[] )
       { 
          // Create an empty account
          Account acc1 = new Account();

          // Create an account with a balance
          Account acc2 = new Account( 5000.0 );

       }

}