Prototype Pattern

We’re going to create an abstract class Shape and concrete classes extending the Shapeclass. A class ShapeCache is defined as a next step which stores shape objects in aHashtable and returns their clone when requested.

PrototypPatternDemo, our demo class will use ShapeCache class to get a Shape object.

Prototype Pattern UML Diagram

Step 1

Create an abstract class implementing Clonable interface.

Shape.java

public abstract class Shape implements Cloneable {
   
   private String id;
   protected String type;
   
   abstract void draw();
   
   public String getType(){
      return type;
   }
   
   public String getId() {
      return id;
   }
   
   public void setId(String id) {
      this.id = id;
   }
   
   public Object clone() {
      Object clone = null;
      
      try {
         clone = super.clone();
         
      } catch (CloneNotSupportedException e) {
         e.printStackTrace();
      }
      
      return clone;
   }
}

Step 2

Create concrete classes extending the above class.

Rectangle.java

public class Rectangle extends Shape {

   public Rectangle(){
     type = "Rectangle";
   }

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

Square.java

public class Square extends Shape {

   public Square(){
     type = "Square";
   }

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

Circle.java

public class Circle extends Shape {

   public Circle(){
     type = "Circle";
   }

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

Step 3

Create a class to get concrete classes from database and store them in a Hashtable.

ShapeCache.java

import java.util.Hashtable;

public class ShapeCache {
	
   private static Hashtable<String, Shape> shapeMap  = new Hashtable<String, Shape>();

   public static Shape getShape(String shapeId) {
      Shape cachedShape = shapeMap.get(shapeId);
      return (Shape) cachedShape.clone();
   }

   // for each shape run database query and create shape
   // shapeMap.put(shapeKey, shape);
   // for example, we are adding three shapes
   
   public static void loadCache() {
      Circle circle = new Circle();
      circle.setId("1");
      shapeMap.put(circle.getId(),circle);

      Square square = new Square();
      square.setId("2");
      shapeMap.put(square.getId(),square);

      Rectangle rectangle = new Rectangle();
      rectangle.setId("3");
      shapeMap.put(rectangle.getId(), rectangle);
   }
}

Step 4

PrototypePatternDemo uses ShapeCache class to get clones of shapes stored in aHashtable.

PrototypePatternDemo.java

public class PrototypePatternDemo {
   public static void main(String[] args) {
      ShapeCache.loadCache();

      Shape clonedShape = (Shape) ShapeCache.getShape("1");
      System.out.println("Shape : " + clonedShape.getType());		

      Shape clonedShape2 = (Shape) ShapeCache.getShape("2");
      System.out.println("Shape : " + clonedShape2.getType());		

      Shape clonedShape3 = (Shape) ShapeCache.getShape("3");
      System.out.println("Shape : " + clonedShape3.getType());		
   }
}

Step 5

Verify the output.

Shape : Circle
Shape : Square
Shape : Rectangle