備忘錄模式 Memento Pattern

Class: Originator

package memento;

class Originator {
	private String state;

	public void set(String state) {
		System.out.println("Originator: Setting state to " + state);
		this.state = state;
	}

	public Memento saveToMemento() {
		System.out.println("Originator: Saving to Memento.");
		return new Memento(state);
	}

	public void restoreFromMemento(Memento m) {
		state = m.getSavedState();
		System.out.println("Originator: State after restoring from Memento: " + state);
	}
}

Class: Memento

package memento;

import java.util.*;

class Memento {
	private String state;

	public Memento(String stateToSave) {
		state = stateToSave;
	}

	public String getSavedState() {
		return state;
	}
}

Class: CareTaker

package memento;

import java.util.ArrayList;

class Caretaker {
	private ArrayList<Memento> savedStates = new ArrayList<Memento>();

	public void addMemento(Memento m) {
		savedStates.add(m);
	}

	public Memento getMemento(int index) {
		return savedStates.get(index);
	}
}

Class: MementoExample

package memento2;

class MementoExample {
	public static void main(String[] args) {
		Originator originator = new Originator();
		Caretaker caretaker = new Caretaker();

		originator.set("State1");
		originator.set("State2");
		caretaker.addMemento(originator.saveToMemento());
		originator.set("State3");
		caretaker.addMemento(originator.saveToMemento());
		originator.set("State4");

		originator.restoreFromMemento(caretaker.getMemento(1));
	}
}

Result:

Originator: Setting state to State1
Originator: Setting state to State2
Originator: Saving to Memento.
Originator: Setting state to State3
Originator: Saving to Memento.
Originator: Setting state to State4
Originator: State after restoring from Memento: State3