Factory pattern is one of the most used design patterns in Java.

This type of design pattern comes under creational pattern.

 

Below is the diagram on the factory design pattern along with the code:

Step 1. Create Shape interface

public interface Shape {   void draw();}

Step 2. Create concrete classes implementing the same interface. As drawn on the above image,

　　Circle class, Square Class, and Rectangle Class.

public class Rectangle implements Shape {   @Override   public void draw() {      System.out.println("Inside Rectangle::draw() method.");   }}

public class Square implements Shape {   @Override   public void draw() {      System.out.println("Inside Square::draw() method.");   }}

public class Circle implements Shape {   @Override   public void draw() {      System.out.println("Inside Circle::draw() method.");   }}

 

Step 3. Create a Factory to generate object of concrete class based on the given information dynamically.

Shape Factory.

public class ShapeFactory {       //use getShape method to get object of type shape    public Shape getShape(String shapeType){      if(shapeType == null){         return null;      }              if(shapeType.equalsIgnoreCase("CIRCLE")){         return new Circle();               } else if(shapeType.equalsIgnoreCase("RECTANGLE")){         return new Rectangle();               } else if(shapeType.equalsIgnoreCase("SQUARE")){         return new Square();      }            return null;   }}

Step 4.

Use the Factory to get object of concrete class by passing an information such as type.

FactoryPatternDemo.java

public class FactoryPatternDemo {   public static void main(String[] args) {      ShapeFactory shapeFactory = new ShapeFactory();      //get an object of Circle and call its draw method.      Shape shape1 = shapeFactory.getShape("CIRCLE");      //call draw method of Circle      shape1.draw();      //get an object of Rectangle and call its draw method.      Shape shape2 = shapeFactory.getShape("RECTANGLE");      //call draw method of Rectangle      shape2.draw();      //get an object of Square and call its draw method.      Shape shape3 = shapeFactory.getShape("SQUARE");      //call draw method of square      shape3.draw();   }}