Description

The Factory Method design pattern is one of the Creational Design Patterns, which is widely used in JDK, Spring, and Struts.

  • It is used to create objects without exposing the creation logic to the client and refer to the created object using a common interface.
  • It is used when we have a superclass with multiple subclasses, and one of the subclasses must be returned based on the input.
  • It is one of the most used design patterns in Java.

Implementation in Java

Let's follow the below approach to implement this design pattern in Java.

  • Create a class and make it an interface.
  • Create multiple subclasses and implement the above interface.
  • Create a factory that contains a method, which invokes a method from the interface to create an object of any of the subclasses types using an input.

Step 1: Create an interface.

Shape.java

public interface Shape {
    void draw();
}

Step 2: Create multiple concrete classes, all implementing the same interface.

Reactangle.java

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

Square.java

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

Circle.java

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

Step 3: Create a factory with a method that generates an object of a concrete class, based on given information.

ShapeFactory.java

public class ShapeFactory {
    //Method to get an object based on the 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: Generate concrete class objects by invoking the Factory method.

public class FactoryPatternDemo {
    public static void main(String[] args) {
        //Get an object of Factory
        ShapeFactory shapeFactory = new ShapeFactory();

        //Get an object of Circle and call its draw method.
        Shape shape1 = shapeFactory.getShape("CIRCLE");
        shape1.draw();

        //Get an object of Rectangle and call its draw method.
        Shape shape2 = shapeFactory.getShape("RECTANGLE");
        shape2.draw();

        //Get an object of Square and call its draw method.
        Shape shape3 = shapeFactory.getShape("SQUARE");
        shape3.draw();
   }
}

Step 5: Execute the code to verify the output.

Inside Circle::draw() method.
Inside Rectangle::draw() method.
Inside Square::draw() method.

Overall

We now know about the Factory Method design pattern and its use cases.

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