备忘录模式

骑猪看日落 2022-05-31 09:26 243阅读 0赞

## 1.使用场景: ##

一系列的操作之后恢复原来的状态。实际的使用场景有事务的回滚操作等。

## 2.UML表示 ##

在备忘录模式中有以下的几种对象:  
2.1源发器:Originator  
2.2备忘录类:Memento  
2.3负责人CareTake  
具体的UML示意图如下：

![20180218161125045][]

## 3.代码实现 ##

首先定义Emp类:

public class Emp {
        private String name;
        private int age;
        private double salary;
    
        public Emp(String name, int age, double salary) {
            this.name = name;
            this.age = age;
            this.salary = salary;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public int getAge() {
            return age;
        }
    
        public void setAge(int age) {
            this.age = age;
        }
    
        public double getSalary() {
            return salary;
        }
    
        public void setSalary(double salary) {
            this.salary = salary;
        }
        //进行备忘录操作
        public EmpMemento memento(){
            return new EmpMemento(this);
        }
        //进行数据恢复,恢复成备忘录对象的值
        public void recovery(EmpMemento emto){
            this.name=emto.getName();
            this.age=emto.getAge();
            this.salary=emto.getSalary();
        }
    }

定义EmpMemento类:

public class EmpMemento {
        private String name;
        private int age;
        private double salary;
    
        public EmpMemento(Emp e) {//这是关键
            this.name=e.getName();
            this.age=e.getAge();
            this.salary=e.getSalary();
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public int getAge() {
            return age;
        }
    
        public void setAge(int age) {
            this.age = age;
        }
    
        public double getSalary() {
            return salary;
        }
    
        public void setSalary(double salary) {
            this.salary = salary;
        }
    
    }

编写CareTaker类:

public class CareTaker {
        private EmpMemento memento;
        public EmpMemento getMemento() {
            return memento;
        }
    
        public void setMemento(EmpMemento memento) {
            this.memento = memento;
        }
    
    }

最后给出测试类:

public class Client {
        public static void main(String[] args) {
            CareTaker careTaker=new CareTaker();
            Emp emp=new Emp("小强",90,900);
            System.out.println(emp.getName()+" "+emp.getAge()+" "+emp.getSalary());
            careTaker.setMemento(emp.memento());
            emp.setAge(9);
            System.out.println(emp.getName()+" "+emp.getAge()+" "+emp.getSalary());
            emp.recovery(careTaker.getMemento());
            System.out.println(emp.getName()+" "+emp.getAge()+" "+emp.getSalary());
        }
    }

## 4.总结 ##

备忘录模式保存了内部状态的拷贝，以后直接恢复即可。  
代码地址:  
[https://github.com/][https_github.com][memoryexplosion][][/design\_pattern\_review/tree/master/src/java/memeto][https_github.com]

[20180218161125045]: /images/20220531/a0fef9beff254d898cb017e35c8c1f16.png
[https_github.com]: https://github.com/saiJPlus/design_pattern_review/tree/master/src/java/memeto
[memoryexplosion]: https://memoryexplosion.github.io/