Código de ejemplo

package model;

public abstract class Shape implements Cloneable {

    protected double area;

    public abstract void calculateArea();

    public double getArea() {
        return area;
    }

    @Override
    public Object clone() {
        Object clone = null;
        try {
            clone = super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return clone;
    }

    @Override
    public String toString() {
        return "Shape{" + "area=" + area + '}';
    }

}

package model;

import static java.lang.Math.PI;
import static java.lang.Math.pow;


public class Circle extends Shape {
    
    private double radious;
    
    public Circle() {
        
    }
    
    public Circle(double radious) {
        this.radious = radious;
    } 
    
    @Override
    public void calculateArea() {
        area = pow(radious, 2) * PI;
    }

    public void setRadious(double radious) {
        this.radious = radious;
    }

    public double getRadious() {
        return radious;
    }  

    @Override
    public String toString() {
        return super.toString() + " Circle{" + "radious=" + radious + '}';
    }
    
}

package model;

public class Square extends Shape {

    private double side;
    
    public Square() {
        
    }   

    public Square(double side) {
        this.side = side;
    }
    
    @Override
    public void calculateArea() {
        area = side * side;
    }
    
    public double getSide() {
        return side;
    }

    public void setSide(double side) {
        this.side = side;
    }

    @Override
    public String toString() {
        return super.toString() + " Square{" + "side=" + side + '}';
    }   
    
}

package model;

public class Rectangle extends Shape {

    private double height;
    private double width; 
    
    public Rectangle() {
        
    }   

    public Rectangle(double height, double width) {
        this.height = height;
        this.width = width;
    }
    
    @Override
    public void calculateArea() {
        area = height * width;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        this.width = width;
    }

    @Override
    public String toString() {
        return super.toString() + " Rectangle{" + "height=" + height + ", width=" + width + '}';
    }    
    
}

package logic;

import java.util.Hashtable;
import model.*;

public enum ShapeCache {
    INSTANCE;

    private Hashtable<String, Shape> shapeMap = new Hashtable<String, Shape>();

    public Shape getShape(String shapeType) {
        Shape shape = shapeMap.get(shapeType);
        if (shapeMap.get(shapeType) != null) {
            return (Shape) shape.clone();
        }
        try {
            String packName = Shape.class.getPackage().getName();
            shape = (Shape) Class.forName(packName + "." + shapeType).newInstance();
            shapeMap.put(shapeType, shape);
            return (Shape) shape.clone();
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
            System.out.println(e.toString());
        }
        return shape;
    }
}

package prototype;

import logic.ShapeCache;
import model.Circle;
import model.Rectangle;
import model.Square;

public class Prototype {

    public static void main(String[] args) {        
        ShapeCache cache = ShapeCache.INSTANCE;
        Circle circle = (Circle) cache.getShape("Circle");
        circle.setRadious(3);
        circle.calculateArea();   
        System.out.println(circle.toString());
        Rectangle rectangle = (Rectangle) cache.getShape("Rectangle");
        rectangle.setHeight(2);
        rectangle.setWidth(3);
        rectangle.calculateArea();
        System.out.println(rectangle.toString());
        Square square = (Square) cache.getShape("Square");
        square.setSide(3);
        square.calculateArea();
        System.out.println(square.toString());
        Circle circle2 = (Circle) cache.getShape("Circle");
        System.out.println(circle2.toString());
        
    }

}