Factory Pattern is a creational pattern as it is used for creating an object. This pattern allows to create an object without exposing the creation logic to the client and refer to newly created object using a common interface.
For instance, let’s create a Shape interface and concrete classes implementing the Shape interface. A factory class ShapeFactory is defined as a next step. See the following scheme:
1. Create an interface
public interface Shape { void draw(); }
2. Create concrete classes implementing the same interface
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."); } }
3. Create a factory to generate object of concrete class based on given information
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; } }
4. Use the Factory to get object of concrete class by passing an information such as type
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(); } }
The output will be :
Inside Circle::draw() method. Inside Rectangle::draw() method. Inside Square::draw() method.