备忘录设计模式（memento）

备忘录就是用来对一个对象进行备份，然后可以恢复回去。

备忘录设计模式：保存某个对象的内部状态的拷贝，以便恢复状态。

结构：发源器类Originator，备忘录类Memento，负责人CareTaker

代码演示备忘录：

1.数据源对象Emp

public class Emp {
    private String ename;
    private int age;
    private double salary;

    

    public EmpMemento memento(){
        return new EmpMemento(this);
    }

    
    public void recovery(EmpMemento mmt){
        this.ename=mmt.getEname();
        this.age=mmt.getAge();
        this.salary=mmt.getSalary();
    }


    public Emp(String ename, int age, double salary) {
        this.ename = ename;
        this.age = age;
        this.salary = salary;
    }

    public Emp() {
    }

    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 double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    @Override
    public String toString() {
        return "Emp{" +
                "ename='" + ename + ''' +
                ", age=" + age +
                ", salary=" + salary +
                '}';
    }
}

2.备忘录对象EmpMemento

public class EmpMemento {
    private String ename;
    private int age;
    private double salary;

    public EmpMemento(Emp 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 double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }
}

3.负责人对象：

public class CareTaker {
    private EmpMemento empMemento;

    
    //private List list=new ArrayList<>();

    public EmpMemento getEmpMemento() {
        return empMemento;
    }

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

4.测试：

 public static void main(String[] args) {
        CareTaker taker=new CareTaker();

        Emp emp=new Emp("杨过",38,40000);
        System.out.println("开始："+emp);

        //备忘一次
        taker.setEmpMemento(emp.memento());

        emp.setAge(40);
        System.out.println("改变："+emp);

        //恢复
        emp.recovery(taker.getEmpMemento());

        System.out.println("恢复："+emp);
    }

结果：

开始：Emp{ename='杨过', age=38, salary=40000.0}
改变：Emp{ename='杨过', age=40, salary=40000.0}
恢复：Emp{ename='杨过', age=38, salary=40000.0}

应用场景：事务回滚等。