备忘录模式

1 解决问题：

一些对象的状态可能需要“回滚”，

于是用一个“memoto”保存原状态，必要的时候再返回

 

2 解决方法：

一个备忘录的生成者Original类，它其实就是那个“可能需要回滚状态”的类。里面有一个creatMemoto（）方法和一个rollbackByMemoto（）方法

一个备忘录类Memoto，存储Original对象的状态

一个备忘录的管理类CareTaker（），用于保管Memoto（封装）。它有一个memoto的域，并提供setter和getter

形如：

Original

public class Original {
	private String state1;
	private String state2;
	public Memoto creatMemoto(){
		Memoto m = new Memoto();
		m.setState1(state1);
		m.setState2(state2);
		return m;
	}
	public void rollbackByMemoto(Memoto m){
		this.state1 = m.getState1();
		this.state2 = m.getState2();
	}
	public String getState1() {
		return state1;
	}
	public void setState1(String state1) {
		this.state1 = state1;
	}
	public String getState2() {
		return state2;
	}
	public void setState2(String state2) {
		this.state2 = state2;
	}
	public Original(String state1, String state2) {
		super();
		this.state1 = state1;
		this.state2 = state2;
	}
	@Override
	public String toString() {
		return this.state1 + " - " + this.state2;
	}
}

 Memoto

public class Memoto {
	private String state1;
	private String state2;

	public String getState1() {
		return state1;
	}
	public void setState1(String state1) {
		this.state1 = state1;
	}
	public String getState2() {
		return state2;
	}
	public void setState2(String state2) {
		this.state2 = state2;
	}
}

 CareTaker

public class CareTaker {
	Memoto memoto ;

	public Memoto getMemoto() {
		return memoto;
	}

	public void setMemoto(Memoto memoto) {
		this.memoto = memoto;
	}
}

 Client

 

public class Demo {
	public static void main(String[] args) {
		Original o = new Original("11","22");
		CareTaker t = new CareTaker();
		t.setMemoto(o.creatMemoto());
		System.out.println(o);
		
		o.setState1("33");
		o.setState2("44");
		System.out.println(o);
		
		o.rollbackByMemoto(t.getMemoto());
		System.out.println(o);
	}
}

 

 

======================进阶===========================

4问题提出：

在第一篇备忘录模式里，Memoto可以给Original和外界同样的权限，这是违反封装原则的。

 

5 解决方法：

宽接口和窄接口

两种思路：

a 对Memoto实现不同权限的接口

b 使用内部类

 

6 实现：

第一种：

如何实现？？？

 

第二种：

public class Original {
	private String state1;
	private String state2;
	public Memoto creatMemoto(){
		Memoto m = new Memoto();
		m.setState1(state1);
		m.setState2(state2);
		return m;
	}
	public void rollbackByMemoto(NerrowMemoto m){
		
		this.state1 = ((Memoto)m).getState1();
		this.state2 = ((Memoto)m).getState2();
	}
	public String getState1() {
		return state1;
	}
	public void setState1(String state1) {
		this.state1 = state1;
	}
	public String getState2() {
		return state2;
	}
	public void setState2(String state2) {
		this.state2 = state2;
	}
	public Original(String state1, String state2) {
		super();
		this.state1 = state1;
		this.state2 = state2;
	}
	@Override
	public String toString() {
		return this.state1 + " - " + this.state2;
	}
	
	//*********inner class********************
	protected class Memoto implements NerrowMemoto{
		private String state1;
		private String state2;

		private String getState1() {
			return state1;
		}

		private void setState1(String state1) {
			this.state1 = state1;
		}

		private String getState2() {
			return state2;
		}

		private void setState2(String state2) {
			this.state2 = state2;
		}
	}
}

 

public interface NerrowMemoto  {

}

 

public class CareTaker {
	NerrowMemoto memoto ;

	public NerrowMemoto getMemoto() {
		return memoto;
	}

	public void setMemoto(NerrowMemoto memoto) {
		this.memoto = memoto;
	}
}

 

public class Demo {
	public static void main(String[] args) {
		Original o = new Original("11","22");
		CareTaker t = new CareTaker();
		t.setMemoto(o.creatMemoto());
		System.out.println(o);
		
		o.setState1("33");
		o.setState2("44");
		System.out.println(o);
		
		o.rollbackByMemoto(t.getMemoto());
		System.out.println(o);
	}
}