Javaファクトリーデザインパターン講座の詳しい解説

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

Rectangle.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.");
   }
}

ShapeFactory.java
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;
   }
}

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 circle
      shape3.draw();
   }
}

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