多次撤銷
改進課堂上的“使用者資訊操作撤銷”例項，使得系統可以實現多次撤銷（可以使用HashMap、ArrayList等集合資料結構實現）。

類圖

程式碼

Java

package rjsj.no20;

public class Client {
    public static void main(String[] args) {
        User user = new User();
        Caretaker caretaker = new Caretaker();

        user.setId("20193288");
        user.setPassword(
 
"123456");
        caretaker.setMemo(user.saveState());
        System.out.println("״̬һ");
        user.show();
        System.out.println("************************************************************");

        user.setId("20193288");
        user.setPassword("qwerasdfzxcv");
        caretaker.setMemo(user.saveState());
        System.out.println(
 
"״̬¶þ");
        user.show();
        System.out.println("************************************************************");

        user.setId("20183288");
        user.setPassword("66666666");
        caretaker.setMemo(user.saveState());
        System.out.println("״̬Ƚ");
        user.show();
        System.out.println(
 
"************************************************************");

        System.out.println("ְ²½³·Ϻ²ٗ÷£º");
        System.out.println("»ָ´µ½״̬¶þ");
        user.restoreState(caretaker.getMemo());
        user.show();
        System.out.println("************************************************************");

        System.out.println("»ָ´µ½״̬һ");
        user.restoreState(caretaker.getMemo());
        user.show();
    }
}

package rjsj.no20;

public class Memo {
    private String id;
    private String password;

    public Memo(String id, String password) {
        this.id = id;
        this.password = password;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

package rjsj.no20;

public class User {
    private String id;
    private String password;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Memo saveState(){
        return new Memo(id,password);
    }

    public void restoreState(Memo m){
        this.id = m.getId();
        this.password = m.getPassword();
    }

    public void show(){
        System.out.println("id:" + this.id);
        System.out.println("password:" + this.password);
    }
}

package rjsj.no20;

import java.util.ArrayList;
import java.util.List;

public class Caretaker {
    private List<Memo> list = new ArrayList<>();

    public void setMemo(Memo m){
        list.add(m);
    }

    public Memo getMemo(){
        Memo m = list.get( list.size() - 2 );
        list.remove( list.size() - 2 );
        return m;
    }
}

C++

#include<iostream>
#include <list>
using namespace std;
class Memento {
private:
    string account;
    string password;
public:
    string getAccount() {
        return account;
    }
    void setAccount(string account) {
        this->account = account;
    }
    string getPassword() {
        return password;
    }
    void setPassword(string password) {
        this->password = password;
    }
    Memento(string account, string password) {
        this->account = account;
        this->password = password;
    }
};
class UserInfoDTO {
private:
    string account;
    string password;
public:
    string getAccount() {
        return account;
    }
    void setAccount(string account) {
        this->account = account;
    }
    string getPassword() {
        return password;
    }
    void setPassword(string password) {
        this->password = password;
    }

    Memento* saveMemento() {
        return new Memento(account,password);
    }
    void restoreMemento(Memento *memento) {
        this->account=memento->getAccount();
        this->password=memento->getPassword();
    }
    void show() {
        cout<<"Account:"<<this->account<<endl;
        cout<<"Password:"<<this->password<<endl;
    }
};
class Caretaker {
private:
    list<Memento*> ll;
public:
    Memento* getMemento() {
        ll.pop_front();
        Memento* mm=ll.front();
        return mm;
    }
    void setMemento(Memento *memento) {
        ll.push_front(memento);
    }
};
int main(){
        UserInfoDTO *user=new UserInfoDTO();
        Caretaker *c=new Caretaker();

        user->setAccount("張三");
        user->setPassword("123456");
        cout<<"狀態一:"<<endl;
        user->show();
        c->setMemento(user->saveMemento());
        cout<<"-----------------------------"<<endl;

        user->setAccount("李四");
        user->setPassword("lisi666");
        cout<<"狀態二:"<<endl;
        user->show();
        c->setMemento(user->saveMemento());
        cout<<"-----------------------------"<<endl;

        user->setAccount("王五");
        user->setPassword("88888888");
        cout<<"狀態三:"<<endl;
        user->show();
        c->setMemento(user->saveMemento());
        cout<<"-----------------------------"<<endl;


        user->restoreMemento(c->getMemento());
        cout<<"回到狀態二:"<<endl;
        user->show();
        cout<<"-----------------------------"<<endl;

        user->restoreMemento(c->getMemento());
        cout<<"回到狀態一:"<<endl;
        user->show();
        cout<<"-----------------------------"<<endl;
}

執行截圖