本次实验属于模仿型实验，通过本次实验学生将掌握以下内容： 

1、理解备忘录模式的动机，掌握该模式的结构；

2、能够利用备忘录模式解决实际问题。

[实验任务一]：多次撤销

改进课堂上的“用户信息操作撤销”实例，使得系统可以实现多次撤销（可以使用HashMap、ArrayList等集合数据结构实现）。

实验要求：

1. 提交源代码；

2. 注意编程规范。

package org.example.shiyan20;

public class main {
    public static void main(String args[]) {
        UserInfoDTO user = new UserInfoDTO();
        Caretaker c = new Caretaker();
        user.setAccount("zhangsan");
        user.setPassword("123456");
        user.setTelNo("130000");
        System.out.println("状态一：");
        user.show();
        c.addMemento(user.saveMemento());
        System.out.println("-----------------");

        user.setPassword("111111");
        user.setTelNo("130111");
        System.out.println("状态二：");
        user.show();
        c.addMemento(user.saveMemento());
        System.out.println("-----------------");

        user.setPassword("222222");
        user.setTelNo("130222");
        System.out.println("状态三：");
        user.show();
        System.out.println("-----------------");

        user.restoreMemento(c.preMemento());
        System.out.println("回到状态二：");
        user.show();
        System.out.println("-----------------");

        user.restoreMemento(c.preMemento());
        System.out.println("回到状态一：");
        user.show();
        System.out.println("-----------------");
    }
}

//Caretaker.java
package org.example.shiyan20;
public class Caretaker
{
    private Memento[] array = null;
    private int index;
    private Memento memento;
    public Memento getMemento()
    {
        return memento;
    }
    public void setMemento(Memento memento)
    {
        this.memento=memento;
    }
    public Caretaker(){
        array = new Memento[10];
        index = 0;
    }
    public void addMemento(Memento Memento){
        array[index++] = Memento;
    }
    public Memento preMemento(){
        Memento pop = null;
        try {
            pop = array[--index];
        } catch (Exception e) {
            e.printStackTrace();
        }
        return pop;
    }
}

package org.example.shiyan20;

class Memento {
    private String account;
    private String password;
    private String telNo;

    public Memento(String account, String password, String telNo) {
        this.account = account;
        this.password = password;
        this.telNo = telNo;
    }

    public String getAccount() {
        return account;
    }

    public void setAccount(String account) {
        this.account = account;
    }

    public String getPassword() {
        return password;
    }

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

    public String getTelNo() {
        return telNo;
    }

    public void setTelNo(String telNo) {
        this.telNo = telNo;
    }
}

package org.example.shiyan20;

public class UserInfoDTO {
    private String account;
    private String password;
    private String telNo;

    public String getAccount() {
        return account;
    }

    public void setAccount(String account) {
        this.account = account;
    }

    public String getPassword() {
        return password;
    }

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

    public String getTelNo() {
        return telNo;
    }

    public void setTelNo(String telNo) {
        this.telNo = telNo;
    }

    public Memento saveMemento() {
        return new Memento(account, password, telNo);
    }

    public void restoreMemento(Memento memento) {
        this.account = memento.getAccount();
        this.password = memento.getPassword();
        this.telNo = memento.getTelNo();
    }

    public void show() {
        System.out.println("账号是" + this.account);
        System.out.println("密码是" + this.password);
        System.out.println("电话是" + this.telNo);
    }
}