Design Patterns in Java (Creational) - Prototype Pattern

Prototype Pattern

• Avoid costly creation
• Typically doesn't use "new"
• Although each copy is a unique instance
• Can utilize parameters in the constructor
• Usually implement a registry
• Usually return a clone object from the registry

Ex.

• Create an abstract class
• implements Cloneable

public abstract class Item implements Cloneable {

    private String item;

    private double price;

    @Override

    protected Object clone() throws CloneNotSupportedException {

        return super.clone();

    }

    public String getItem() {

        return item;

    }

    public void setItem(String item) {

        this.item = item;

    }

    public double getPrice() {

        return price;

    }

    public void setPrice(double price) {

        this.price = price;

    }

}

• Create the inherited classes

public class Movie extends Item {

    private String name;

    

   

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

• Create the Registry, the core of the pattern

public class Registry {

    

    private Map<String, Item> items = new HashMap<String, Item>();

    

    public Registry(){

        loadItems();

    }

    

    private void loadItems(){

        Movie movie = new Movie();

        movie.setName("Quijote");

        Toys toy = new Toys();

        toy.setAge(12);

        

        items.put("Movie", movie);

        items.put("Toy", toy);

    }

    

    public Item createItem(String type){

        Item item = null;

        

        try{

            item = (Item)(items.get(type)).clone();

        }catch(CloneNotSupportedException e){

            e.printStackTrace();

        }

        item = items.get(type);

        

        return item;

    }

}

• Execute the pattern

public static void main(String[] args) {

        

        Registry registry = new Registry();

        

        Movie movie = (Movie)registry.createItem("Movie");

        movie.setName("A");

        

        Movie movie2 = (Movie)registry.createItem("Movie");

        movie2.setName("A");

        

    }