设计模式--备忘录模式

                 设计模式--备忘录模式

 

•备忘录模式原理

•讨论一个游戏进度状态保存问题
 

游戏进度保存：对象状态，场景...

想想有哪些方式：

SharedPreferences、Sqlite、Server

思考如何设计

 

•备忘录模式原理




备忘录模式：在不破坏封装的前提下，存储关键对象的重要状态，从而可以在将来把对象还原到存储的那个状态

•备忘录模式优缺点

优点：

  状态存储在外面，不和关键对象混在一起，这可以帮助维护内聚 

  提供了容易实现的恢复能力

  保持了关键对象的数据封装

缺点：

  资源消耗上面备忘录对象会很昂贵

  存储和恢复状态的过程比较耗时

•备忘录模式示例代码讲解


MementoIF 

public interface MementoIF {

}

MementoCaretaker  

import java.util.HashMap;

public class MementoCaretaker {
	private HashMap<String, MementoIF> mementomap;

	public MementoCaretaker() {
		mementomap = new HashMap<String, MementoIF>();
	}

	public MementoIF retrieveMemento(String name) {
		return mementomap.get(name);
	}

	/**
	 * 备忘录赋值方法
	 */
	public void saveMemento(String name, MementoIF memento) {
		this.mementomap.put(name, memento);
	}
}

Originator 

import java.util.HashMap;

public class Originator {
	private HashMap<String, String> state;

	public Originator() {
		state = new HashMap();

	}

	public MementoIF createMemento() {
		return new Memento(state);
	}

	public void restoreMemento(MementoIF memento) {
		state = ((Memento) memento).getState();
	}

	public void showState() {
		System.out.println("now state:" + state.toString());
	}

	public void testState1() {
		state.put("blood", "500");
		state.put("progress", "gate1 end");
		state.put("enemy", "5");

	}

	public void testState2() {
		state.put("blood", "450");
		state.put("progress", "gate3 start");
		state.put("enemy", "3");

	}

	private class Memento implements MementoIF {

		private HashMap<String, String> state;

		private Memento(HashMap state) {
			this.state = new HashMap(state);
		}

		private HashMap getState() {
			return state;
		}

		private void setState(HashMap state) {
			this.state = state;
		}
	}
}

Originator2 

import java.util.ArrayList;

public class Originator2 {
	private ArrayList<String> state;

	public Originator2() {
		state = new ArrayList<String>();
	}

	public MementoIF createMemento() {
		return new Memento(state);
	}

	public void restoreMemento(MementoIF memento) {
		state = ((Memento) memento).getState();
	}

	public void testState1() {
		state = new ArrayList<String>();
		state.add("blood:320");
		state.add("progress:gate2 mid");
		state.add("enemy:15");

	}

	public void testState2() {
		state = new ArrayList<String>();
		state.add("blood:230");
		state.add("progress:gate8 last");
		state.add("enemy:12");

	}

	public void showState() {
		System.out.println("now state:" + state.toString());
	}

	private class Memento implements MementoIF {

		private ArrayList<String> state;

		private Memento(ArrayList<String> state) {
			this.state = new ArrayList(state);
		}

		private ArrayList<String> getState() {
			return state;
		}

		private void setState(ArrayList<String> state) {
			this.state = state;
		}
	}

}

MainTest 

public class MainTest {

	public static void main(String[] args) {
		MementoCaretaker mMementoCaretaker = new MementoCaretaker();
		Originator mOriginator = new Originator();
		Originator2 mOriginator2 = new Originator2();
		
		System.out.println("*****Originator*****");
		mOriginator.testState1();
		mMementoCaretaker
				.saveMemento("Originator", mOriginator.createMemento());
		mOriginator.showState();
		mOriginator.testState2();
		mOriginator.showState();
		mOriginator.restoreMemento(mMementoCaretaker
				.retrieveMemento("Originator"));
		mOriginator.showState();

		System.out.println("*****Originator 2*****");
		mOriginator2.testState1();
		mOriginator2.showState();
		mMementoCaretaker.saveMemento("Originator2",
				mOriginator2.createMemento());
		mOriginator2.testState2();
		mOriginator2.showState();
		mOriginator2.restoreMemento(mMementoCaretaker
				.retrieveMemento("Originator2"));
		mOriginator2.showState();

		//System.out.println("*****Originator&&Originator 2*****");
	//	 mOriginator.restoreMemento(mMementoCaretaker
	//	 .retrieveMemento("Originator2"));
	//	 mOriginator.showState();

	}

}

•备忘录模式关键点

•备忘录模式原理
备忘录模式：在不破坏封装的前提下，存储关键对象的重要状态，从而可以在将来把对象还原到存储的那个状态

注意事项：

  注意开销

•备忘录模式适用场合

适用场合：

•  必须保存一个对象在某一个时刻的(整体或部分)状态，在对象以外的地方, 以后需要时恢复到先前的状态时