Factory Pattern

• aka “Simple Factory” or “Static Factory Method”
• Java Examples:
  • Calendar
  • NumberFormat
• Note: Use of abstract class vs interface is really not that important
• There is difference b/w of static factory and GoF factory pattern (confusing)
  • https://stackoverflow.com/a/64771815/7801965
• Classes

public interface Shape {
   void draw();
}
 
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.");
   }
}

• Factory

public class ShapeFactory {
   public Shape getShape(String shapeType){
      if(shapeType == null){
         return null;
      }
      if(shapeType.equalsIgnoreCase("RECTANGLE")){
         return new Rectangle();
      
      } else if(shapeType.equalsIgnoreCase("SQUARE")){
         return new Square();
      }
      
      return null;
   }
}

• Driver

public class Demo {
    public static void main(String[] args) {
        ShapeFactory shapeFactory = new ShapeFactory();
        Shape circle = shapeFactory.getShape("CIRCLE");
        Shape rectangle = shapeFactory.getShape("RECTANGLE");
    }
}

UML

• I think ideally the arrow for implements should be empty arrow but I have no idea whether a filled arrow is same or not