具体代码

//Memento.java
package org.example.test018;

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

    private String account;
    private String password;
    private String telNo;
}

//UserInfoDTO.java
package org.example.test018;

public class UserInfoDTO {
    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;
    }

    private String account;
    private String password;
    private String 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("Account:" + this.account);
        System.out.println("Password:" + this.password);
        System.out.println("TelNo:" + this.telNo);
    }
}

//Caretaker.java
package org.example.test018;

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;
    }
}

//Client.java
package org.example.test018;

import javax.security.auth.login.CredentialException;

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

        userInfoDTO.setAccount("zhangsan");
        userInfoDTO.setPassword("123456");
        userInfoDTO.setTelNo("1300000000");
        System.out.println("状态一：");
        userInfoDTO.show();
        caretaker.addMemento(userInfoDTO.saveMemento());
        System.out.println("------------------");

        userInfoDTO.setPassword("111111");
        userInfoDTO.setTelNo("13000000001");
        System.out.println("状态二：");
        userInfoDTO.show();
        caretaker.addMemento(userInfoDTO.saveMemento());
        System.out.println("-------------------");

        userInfoDTO.setPassword("222222");
        userInfoDTO.setTelNo("12222222222");
        System.out.println("状态三：");
        userInfoDTO.show();
        System.out.println("-------------------");

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

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

运行结果