备忘录模式就是保存某个对象内部状态的拷贝，这样就可以将该对象恢复为原来的对象。

结构：

  源发器类；备忘录类；负责人类；

//源发器类
public class Emo {
    private String ename;
    private int age;
    private String salary;
    
    //进行备忘录操作
    public EmpMemento memento(){
        return new EmpMemento(this);
    }
    //进行数据恢复
    public void recovery(EmpMemento em){
        this.ename = em.getEname();
        this.age = em.getAge();
        this.salary = em.getSalary();
    }
    
    
    public Emo(String ename, int age, String salary) {
        super();
        this.ename = ename;
        this.age = age;
        this.salary = salary;
    }
    public String getEname() {
        return ename;
    }
    public void setEname(String ename) {
        this.ename = ename;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getSalary() {
        return salary;
    }
    public void setSalary(String salary) {
        this.salary = salary;
    }
    
}
//备忘录类
public class EmpMemento {
    private String ename;
    private int age;
    private String salary;
    
    
    public EmpMemento(Emo e){
        this.ename = e.getEname();
        this.age = e.getAge();
        this.salary = e.getSalary();
    }

    public String getEname() {
        return ename;
    }
    public void setEname(String ename) {
        this.ename = ename;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getSalary() {
        return salary;
    }
    public void setSalary(String salary) {
        this.salary = salary;
    }
    
    
}
//负责人类
public class CareTake {
    private EmpMemento empMemento;//可以将其保存到容器中 比如Stack

    public EmpMemento getEmpMemento() {
        return empMemento;
    }

    public void setEmpMemento(EmpMemento empMemento) {
        this.empMemento = empMemento;
    }
    
}
public class Client {

    public static void main(String[] args) {
        CareTake careTake = new CareTake();
        Emo emo = new Emo("kobe", 23, "15000");
        System.out.println("第一次打印："+emo.getEname()+" "+emo.getAge()+" "+emo.getSalary());
        careTake.setEmpMemento(emo.memento());    
        emo.setEname("james");
        emo.setAge(33);
        emo.setSalary("15000");
        System.out.println("第二次打印："+emo.getEname()+" "+emo.getAge()+" "+emo.getSalary());
        
        emo.recovery(careTake.getEmpMemento());
        System.out.println("第三次打印："+emo.getEname()+" "+emo.getAge()+" "+emo.getSalary());
    }
}

运行结果：
第一次打印：kobe 23 15000
第二次打印：james 33 18000
第三次打印：kobe 23 15000

应用场景：

棋类游戏中:悔棋

普通软件中：撤销操作

数据库软件中：回滚操作