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我正在尝试保存向量并使用 undo 方法通过使用备忘录模式来恢复向量，但它不起作用。看守者.java：

import java.util.*;
public class Caretaker {
    private Vector <Memento> undoList= new Vector<Memento>();
    public Caretaker() {}
    public void saveMyClass(MyClass mc){
        undoList.add(new Memento(mc));
        }
    
    public void undo(){
        undoList.lastElement().restore();
        undoList.remove(undoList.lastElement());
        }
}

备忘录.java：


public class Memento {
    private MyClass myclass;
    private Vector mState;
    public Memento(MyClass mc) {
        this.myclass=mc;
        mState=mc.state;
    }
    public void restore()
    {
        myclass.state=this.mState;
    }
    
    
}

MyClass.java：


public class MyClass {
Vector state=new Vector<>();
    public MyClass() {
        
    }
    public Vector getState(){
        return state;
        }
    public void doAction(int i){
        state.add(i);
        }
}

TestMemento.java：

    public static void main(String args[]) {
        Caretaker ct = new Caretaker();
        MyClass mc = new MyClass();
        System.out.println("Create a my class object with state 1");
        System.out.println("Current state : " + mc.getState());
        ct.saveMyClass(mc);
        mc.doAction(3);
        System.out.println("Change my class object to state 2");
        System.out.println("Current state : " + mc.getState());
        ct.saveMyClass(mc);
        mc.doAction(5);
        System.out.println("Change my class object to state 3");
        System.out.println("Current state : " + mc.getState());
        ct.saveMyClass(mc);
        mc.doAction(7);
        System.out.println("Change my class object to state 4");
        System.out.println("Current state : " + mc.getState());
        ct.undo();
        System.out.println("Perform undo");
        System.out.println("Current state : " + mc.getState());
        ct.undo();
        System.out.println("Perform undo");
        System.out.println("Current state : " + mc.getState());
    }
}

结果：

Current state : []
Change my class object to state 2
Current state : [3]
Change my class object to state 3
Current state : [3, 5]
Change my class object to state 4
Current state : [3, 5, 7]
Perform undo
Current state : [3, 5, 7]
Perform undo
Current state : [3, 5, 7]

因此，我更喜欢在撤消后更改为之前的状态。但它不起作用。在同样的情况下，我已将 Vector 更改为 int 状态

public void doAction(){
        state++;
        }

然后我可以得到结果

Create my class object with state 1
Current state : 0
Change my class object to state 2
Current state: 1
Change my class object to state 3
Current state: 2
Change my class object to state 4
Current state : 3
Perform undo
Current state: 2
Perform undo 
Current state: 1
4

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