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Prototype pattern: used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects. This pattern is used to:

• avoid subclasses of an object creator in the client application, like the abstract factory pattern does.
• avoid the inherent cost of creating a new object in the standard way (e.g., using the ‘new’ keyword) when it is prohibitively expensive for a given application.

Here is UML diagram for Prototype pattern.



Design Patterns - Prototype


Here is the code examples:

/**
 * The Animal abstract class is the prototype in the "Prototype" Pattern. The
 * animal class contains properties that describe on a abstract level the different
 * prototypes that can exist in the pattern example.
 */
public abstract class Animal implements Cloneable {
	protected int numberOfLegs = 0;
	protected String description = "";
	protected String name = "";
	public abstract String helloAnimal();	

	/**
	 * The clone method creates a clone of the current Animal object.
	 */
	public Animal clone() {
		Animal clonedAnimal = null;
		try {
			clonedAnimal = (Animal) super.clone();
			clonedAnimal.setDescription(description);
			clonedAnimal.setNumberOfLegs(numberOfLegs);
			clonedAnimal.setName(name);

		} catch (CloneNotSupportedException e) {
			e.printStackTrace();
		}
		return clonedAnimal;
	}  

	public String getDescription() {
		return description;
	}

	public void setDescription(String description) {
		this.description = description;
	}

	public int getNumberOfLegs() {
		return numberOfLegs;
	}

	public void setNumberOfLegs(int numberOfLegs) {
		this.numberOfLegs = numberOfLegs;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}

/**
 * The AnimalCreator class is used to create and manage prototype objects. The AnimalCreator
 * class contains two concrete prototypes that is initialized during the initialization of
 * the class. The AnimalCreator class forms part of the "Prototype" pattern by returning
 * a cloned object (Animal) to the client, withou the client knowing the type of the prototype.
 */
public class AnimalCreator {

	private Animal sheep = new Sheep();	

	private Animal chicken = new Chicken();

	public AnimalCreator() {
		sheep.setName("Sheep");
		sheep.setNumberOfLegs(4);
		sheep.setDescription("Four legged creature that makes wool.");

		chicken.setName("Chicken");
		chicken.setNumberOfLegs(2);
		chicken.setDescription("Two legged creature that crosses roads.");
	} 

	public Animal retrieveAnimal(String kindOfAnimal) {
		if ("Chicken".equals(kindOfAnimal)) {
			return (Animal) chicken.clone();
		} else if ("Sheep".equals(kindOfAnimal)) {
			return (Animal) sheep.clone();
		} // if

		return null;
	} // method retrieveAnimal
}

public class Chicken extends Animal {
	private int numberOfClones = 0;
	public String helloAnimal() {
	StringBuffer chickenTalk = new StringBuffer();
	chickenTalk.append("Cluck cluck World. I am ");
	chickenTalk.append(name);
	chickenTalk.append(". I have ");
	chickenTalk.append(numberOfLegs);
	chickenTalk.append(" legs.");
	return chickenTalk.toString();
	} // helloAnimal

	public Chicken clone() {
		Chicken clonedChicken = (Chicken) super.clone();
		String chickenName = clonedChicken.getName();
		numberOfClones++;
		clonedChicken.setName(chickenName + numberOfClones);
		return clonedChicken;
	} // method clone
}

public class Sheep extends Animal {
	private int numberOfClones = 0;
	public String helloAnimal() {
	StringBuffer sheepTalk = new StringBuffer();
	sheepTalk.append("Meeeeeee World. I am ");
	sheepTalk.append(name);
	sheepTalk.append(". I have ");
	sheepTalk.append(numberOfLegs);
	sheepTalk.append(" legs.");
	return sheepTalk.toString();
	}

	public Sheep clone() {
		Sheep clonedSheep = (Sheep) super.clone();
		String sheepName = clonedSheep.getName();
		numberOfClones++;
		clonedSheep.setName(sheepName + numberOfClones);
		return clonedSheep;
	} 

}

and for the end client class

public class AnimalClient {
	public static void main(String[] args) {
		AnimalCreator animalCreator = new AnimalCreator();
		Animal[] animalFarm = new Animal[8];
		animalFarm[0] = animalCreator.retrieveAnimal("Chicken");
		animalFarm[1] = animalCreator.retrieveAnimal("Chicken");
		animalFarm[2] = animalCreator.retrieveAnimal("Chicken");
		animalFarm[3] = animalCreator.retrieveAnimal("Chicken");

		animalFarm[4] = animalCreator.retrieveAnimal("Sheep");
		animalFarm[5] = animalCreator.retrieveAnimal("Sheep");
		animalFarm[6] = animalCreator.retrieveAnimal("Sheep");
		animalFarm[7] = animalCreator.retrieveAnimal("Sheep");

		for (int i= 0; i< =7; i++) {
			System.out.println(animalFarm[i].helloAnimal());
		} // for
	}
}