Sablonul de proiectare Prototype

Sablonul prototype este practic mecanismul de construire a unui obiect prin clonarea unei instante existene. Acest mecanism se utilizeaza atunci cand mecanismul standard de construire a obiectelor prin new este prea costisitor sau nu este permis. Acest sablon utilizeaza metoda Object.clone().

public abstract class Product implements Cloneable {
 
    private String SKU;
    private String description;
 
    public Object clone() {
        Object clone = null;
        try {
            clone = super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return clone;
    }
 
    public String getDescription() {
        return description;
    }
 
    public String getSKU() {
        return SKU;
    }
 
    public void setDescription(String string) {
        description = string;
    }
 
    public void setSKU(String string) {
        SKU = string;
    }
}
 
/**
 * Concrete Prototypes to clone *
 */
class Book extends Product {
 
    private int numberOfPages;
 
    public int getNumberOfPages() {
        return numberOfPages;
    }
 
    public void setNumberOfPages(int i) {
        numberOfPages = i;
    }
}
 
/**
 * Concrete Prototypes to clone *
 */
class DVD extends Product {
 
    private int duration;
 
    public int getDuration() {
        return duration;
    }
 
    public void setDuration(int i) {
        duration = i;
    }
}
 
//////////////////////// PrototypeExample.java
 
import java.util.Hashtable;
 
public class PrototypeExample {
 
    Hashtable<String, Product> productMap = new Hashtable<String, Product>();
 
    public Product getProduct(String productCode) {
        Product cachedProduct
                = (Product) productMap.get(productCode);
        return (Product) cachedProduct.clone();
    }
 
    public void loadCache() {
//for each product run expensive query and instantiate
// product productMap.put(productKey, product);
// for exemplification, we add only two products
        Book b1 = new Book();
        b1.setDescription("Oliver Twist");
        b1.setSKU("B1");
        b1.setNumberOfPages(100);
        productMap.put(b1.getSKU(), b1);
        DVD d1 = new DVD();
        d1.setDescription("Superman");
        d1.setSKU("D1");
        d1.setDuration(180);
        productMap.put(d1.getSKU(), d1);
    }
 
    public static void main(String[] args) {
        PrototypeExample pe = new PrototypeExample();
        pe.loadCache();
        Book clonedBook = (Book) pe.getProduct("B1");
        System.out.println("SKU = " + clonedBook.getSKU());
        System.out.println("SKU = "
                + clonedBook.getDescription());
        System.out.println("SKU = "
                + clonedBook.getNumberOfPages());
        DVD clonedDVD = (DVD) pe.getProduct("D1");
        System.out.println("SKU = " + clonedDVD.getSKU());
        System.out.println("SKU = " + clonedDVD.getDescription());
        System.out.println("SKU = " + clonedDVD.getDuration());
 
    }
}

Rezultatul rularii codului:

SKU = B1
SKU = Oliver Twist
SKU = 100
SKU = D1
SKU = Superman
SKU = 180