備忘錄模式

   在不破壞封裝性的前提下，補貨一個物件的內部狀態，並在改物件之外儲存這個狀態，這樣就可以將現在的狀態恢復到原先儲存的狀態。

模型圖

 程式碼

public class Originator {

	private String state="on";
	
	private Memento memento=null;

	public Memento getMemento() {
		return new Memento(state);
	}

	public void setMemento(Memento memento) {
		this.state=memento.getState();
	}

	public String getState() {
		return state;
	}

	public void setState(String state) {
		this.state = state;
	}
	
	public void showState(){
		System.out.println("狀態:="+this.state);
	}
}
 

public class Memento {
	private String state="on";

	public Memento(String state) {
         this.state=state;
	}
	public String getState() {
		return state;
	}

	public void setState(String state) {
		this.state = state;
	}
}

public class CareTaker {
	private Memento memento;

	public Memento getMemento() {
		return memento;
	}

	public void setMemento(Memento memento) {
		this.memento = memento;
	}
}
 

public class Test {
   public static void main(String[] args) {
	Originator  originator=new Originator();
	originator.setState("on");
	originator.showState();
	
	
	CareTaker careTaker=new CareTaker();
	careTaker.setMemento(originator.getMemento());
    originator.setState("off");
    originator.showState();
    
    
    originator.setMemento(careTaker.getMemento());
    originator.showState();	
	
	   
   }
}
 

 案例 模擬遊戲角色生命存檔

分析設計 通過備忘錄模式進行存檔

模型圖

public class RoleGame {
	//生命力
	private int live;
	//法力
	private int atk;
	//攻擊力
	private int hit;
	
    private RoleStateMemento roleStateMemento=null;
    
	public RoleStateMemento getRoleStateMemento() {
		return new RoleStateMemento(live,atk,hit);
	}
	public void setRoleStateMemento(RoleStateMemento roleStateMemento) {
		this.live=roleStateMemento.getLive();
		this.atk=roleStateMemento.getAtk();
		this.hit=roleStateMemento.getHit();
	}
	public int getLive() {
		return live;
	}
	public void setLive(int live) {
		this.live = live;
	}
	@Override
	public String toString() {
		return "RoleGame [live=" + live + ", atk=" + atk + ", hit=" + hit+"]";
	}
	public int getAtk() {
		return atk;
	}
	public RoleGame(int live, int atk, int hit) {
		super();
		this.live = live;
		this.atk = atk;
		this.hit = hit;
	}
	public void setAtk(int atk) {
		this.atk = atk;
	}
	public int getHit() {
		return hit;
	}
	public void setHit(int hit) {
		this.hit = hit;
	}
	
	
	public void show(){
		System.out.println(toString());
	}
	
	
}

public class RoleGameCareTaker {
    Map<String,RoleStateMemento> memen=new ConcurrentHashMap<String, RoleStateMemento>();
	
	public void savePro(String key,RoleStateMemento value){
		memen.put(key, value);
	}
	
	
	public RoleStateMemento readPro(String key){
		return memen.get(key);
	}
}

public class RoleStateMemento {
	public RoleStateMemento(int live, int atk, int hit) {
		super();
		this.live = live;
		this.atk = atk;
		this.hit = hit;
	}
	//生命力
	private int live;
	//法力
	private int atk;
	//攻擊力
	private int hit;
		
	public int getLive() {
		return live;
	}
	public void setLive(int live) {
		this.live = live;
	}
	public int getAtk() {
		return atk;
	}
	public void setAtk(int atk) {
		this.atk = atk;
	}
	public int getHit() {
		return hit;
	}
	public void setHit(int hit) {
		this.hit = hit;
	}
		
}

public class Test {
 public static void main(String[] args) {
	RoleGame game=new RoleGame(1, 1, 1);
	game.show();
	
	RoleGameCareTaker careTaker=new RoleGameCareTaker();
	careTaker.savePro("1",game.getRoleStateMemento());
	
	game=new RoleGame(2, 2, 2);
	careTaker.savePro("2", game.getRoleStateMemento());
	game.show();
	
	game=new RoleGame(3, 3, 3);
	careTaker.savePro("3", game.getRoleStateMemento());
	game.show();
	
	game.setRoleStateMemento(careTaker.readPro("1"));
	game.show();
	
	game.setRoleStateMemento(careTaker.readPro("2"));
	game.show();
 }
}

結果圖

 小結

1 將物件狀態的細節儲存在備忘錄中 哪天更改備忘錄也不至於影響到原物件。

2 適合功能比較複雜 又要儲存歷史屬性的具體類

3 就是追溯歷史變數的時候