Difference Between Singleton and Factory Design Pattern in Java

Last Updated : 27 Nov, 2023

Design patterns are essential tools for creating maintainable and scalable software. Two commonly used design patterns in Java are the Singleton and Factory patterns. This article provides an introduction to the Singleton and Factory design patterns with examples.

Singleton Design Pattern in Java

The Singleton pattern is a creational design pattern that ensures that only one instance of a class can be created and that the same instance is used every time the object is requested.

Example:

Java

import java.io.*; 
  
public class Singleton { 
    // Private static variable to hold the single instance 
    // of the class 
    private static Singleton instance = null; 
  
    // Private constructor to prevent outside instantiation 
    private Singleton() {} 
  
    // Public static method to get the single instance of 
    // the class 
    public static Singleton getInstance() 
    { 
        if (instance == null) { 
            instance = new Singleton(); 
        } 
        return instance; 
    } 
  
    // Public method to demonstrate the Singleton instance 
    public void showMessage() 
    { 
        System.out.println( 
            "Hello, I am the Singleton instance."); 
    } 
  
    public static void main(String[] args) 
    { 
        // Get the Singleton instance 
        Singleton singleton = Singleton.getInstance(); 
  
        // Call a method on the Singleton instance 
        singleton.showMessage(); 
    } 
}

Output:

Hello, I am the Singleton instance.

Factory Design Pattern in Java

The Factory pattern is a creational pattern that provides a way to create objects without specifying the exact class of object that will be created. It provides a factory method that is responsible for creating objects of the appropriate type based on a set of criteria, such as a type or a configuration parameter.

Example:

Java

import java.io.*; 
  
interface Shape { 
    void draw(); 
} 
  
class Rectangle implements Shape { 
    public void draw() 
    { 
        System.out.println("Drawing a rectangle."); 
    } 
} 
  
class Circle implements Shape { 
    public void draw() 
    { 
        System.out.println("Drawing a circle."); 
    } 
} 
  
class ShapeFactory { 
    // Factory method to create Shape objects based on the 
    // input String 
    public Shape getShape(String shapeType) 
    { 
        if (shapeType == null) { 
            return null; 
        } 
        else if (shapeType.equalsIgnoreCase("rectangle")) { 
            return new Rectangle(); 
        } 
        else if (shapeType.equalsIgnoreCase("circle")) { 
            return new Circle(); 
        } 
        return null; 
    } 
} 
  
public class FactoryPatternExample { 
    public static void main(String[] args) 
    { 
        // Create a ShapeFactory object 
        ShapeFactory shapeFactory = new ShapeFactory(); 
  
        // Get a Rectangle object and call its draw method 
        Shape shape1 = shapeFactory.getShape("rectangle"); 
        shape1.draw(); 
  
        // Get a Circle object and call its draw method 
        Shape shape2 = shapeFactory.getShape("circle"); 
        shape2.draw(); 
    } 
}

Output:

Drawing a rectangle.
Drawing a circle.