Factory Pattern
Author: Deron Eriksson
Description: This Java tutorial describes the factory pattern, a popular creational design pattern.
Tutorial created using: Windows XP || JDK 1.6.0_10 || Eclipse JEE Ganymede SR1 (Eclipse 3.4.1)

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(Continued from page 1)

Now, let's implement our factory. We will call our factory's object creation method getAnimal. This method takes a String as a parameter. If the String is "canine", it returns a Dog object. Otherwise, it returns a Cat object.


package com.cakes;

public class AnimalFactory {

	public Animal getAnimal(String type) {
		if ("canine".equals(type)) {
			return new Dog();
		} else {
			return new Cat();


The Demo class demonstrates the use of our factory. It creates an AnimalFactory factory. The factory creates an Animal object and then another Animal object. The first object is a Cat and the second object is a Dog. The output of each object's makeSound() method is displayed.


package com.cakes;

public class Demo {

	public static void main(String[] args) {
		AnimalFactory animalFactory = new AnimalFactory();

		Animal a1 = animalFactory.getAnimal("feline");
		System.out.println("a1 sound: " + a1.makeSound());

		Animal a2 = animalFactory.getAnimal("canine");
		System.out.println("a2 sound: " + a2.makeSound());


The console output is shown here.

Console Output

a1 sound: Meow
a2 sound: Woof

Notice that the factory has encapsulated our Animal object creation code, thus resulting in clean code in Demo, the class that creates the factory. Additionally, notice the use of polymorphism. We obtain different Animal objects (Cat and Dog) based on data passed to the factory.

Note that it is common to pass data that determines the type of object to be created to the factory when the factory is created (via the factory constructor). However, if multiple objects are being created by the factory, it may make sense to pass this data to the factory's creational method rather than to the constructor, since it might not make sense to create a new factory object each time we wanted to have the factory instantiate a new object.

A factory may also be used in conjunction with the singleton pattern. It is common to have a singleton return a factory instance. To do this, we could replace:

AnimalFactory animalFactory = new AnimalFactory();


AnimalFactory animalFactory = AnimalFactory.getAnimalFactoryInstance();

In this example, AnimalFactory.getAnimalFactoryInstance() would be implemented to return a static AnimalFactory object. This results in a single factory being instantiated and used rather than requiring a new factory to be instantiated each time the factory needs to be used.

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