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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");
        
    }



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