原型模式Prototype

//Purpose.  Prototype design pattern

//1. Create a "contract" with clone() and getName() entries
//2. Design a "registry" that maintains a cache of prototypical objects
//3. Populate the registry with an initializePrototypes() function
//4. The registry has a findAndClone() "virtual constructor" that can transform
// a String into its correct object (it calls clone() which then calls "new")
//5. All classes relate themselves to the clone() contract
//6. Client uses the findAndClone() virtual ctor instead of the "new" operator

interface Prototype {
	Object clone();

	String getName();
} // 1. The clone()

interface Command {
	void execute();
} // contract

class PrototypesModule { // 2. "registry" of prototypical objs
	private static Prototype[] prototypes = new Prototype[9];
	private static int total = 0;

	public static void addPrototype(Prototype obj) {
		prototypes[total++] = obj;
	}

	public static Object findAndClone(String name) { // 4. The "virtual ctor"
		for (int i = 0; i < total; i++)
			if (prototypes[i].getName().equals(name))
				return prototypes[i].clone();
		System.out.println(name + " not found");
		return null;
	}
}

// 5. Sign-up for the clone()
class This implements Prototype, Command { // contract. Each class
	public Object clone() {
		return new This();
	} // calls "new" on itself

	public String getName() {
		return "This";
	} // FOR the client.

	public void execute() {
		System.out.println("This: execute");
	}
}

class That implements Prototype, Command {
	public Object clone() {
		return new That();
	}

	public String getName() {
		return "That";
	}

	public void execute() {
		System.out.println("That: execute");
	}
}

class TheOther implements Prototype, Command {
	public Object clone() {
		return new TheOther();
	}

	public String getName() {
		return "TheOther";
	}

	public void execute() {
		System.out.println("TheOther: execute");
	}
}

public class PrototypeDemo {
	public static void initializePrototypes() { // 3. Populate the "registry"
		PrototypesModule.addPrototype(new This());
		PrototypesModule.addPrototype(new That());
		PrototypesModule.addPrototype(new TheOther());
	}

	public static void main(String[] args) {
		initializePrototypes();
		Object[] objects = new Object[9];
		int total = 0;
		for (int i = 0; i < args.length; i++) { // 6. Client does not use "new"
			objects[total] = PrototypesModule.findAndClone(args[i]);
			if (objects[total] != null)
				total++;
		}
		for (int i = 0; i < total; i++)
			((Command) objects[i]).execute();
	}
}