设计模式 - 备忘录模式(Memento)

Memento模式在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可将该对象恢复到原先保存的状态。

类图：



案例： 购物的时候你可以临时改变送货地址和联系电话，通过Memento模式恢复到原始的送货地址和联系电话。

public class Buyer {
private String name;
private String phoneNum;
private String address;
public Buyer(String name, String phoneNum, String address) {
this.name = name;
this.phoneNum = phoneNum;
this.address = address;
}
public String getName() {
return name;
}
public String getPhoneNum() {
return phoneNum;
}
public void setPhoneNum(String phoneNum) {
this.phoneNum = phoneNum;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public Memento createMemento() {
return new Memento(this.phoneNum, this.address);
}
public void setMemento(Memento memento) {
this.phoneNum = memento.getPhoneNum();
this.address = memento.getAddress();
}
}

public class Memento {
private String phoneNum;
private String address;
public Memento(String phoneNum, String address) {
this.phoneNum = phoneNum;
this.address = address;
}
public String getPhoneNum() {
return phoneNum;
}
public void setPhoneNum(String phoneNum) {
this.phoneNum = phoneNum;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}

测试代码

import org.junit.Test;
import static org.junit.Assert.*;
public class MementoTest {
@Test
public void testMemento(){
Buyer buyer = new Buyer("Tom", "0755-12345678", "Shenzhen");
assertEquals("the original phone number is 0755-12345678", "0755-12345678", buyer.getPhoneNum());
assertEquals("the original address is Shenzhen", "Shenzhen", buyer.getAddress());

Memento memento = buyer.createMemento();

buyer.setPhoneNum("021-88888888");
buyer.setAddress("ShangHai");
assertEquals("the phone number is changed to 021-88888888", "021-88888888", buyer.getPhoneNum());
assertEquals("the original address is changed to ShangHai", "ShangHai", buyer.getAddress());

buyer.setMemento(memento);
assertEquals("the phone number is restored to 0755-12345678", "0755-12345678", buyer.getPhoneNum());
assertEquals("the original address is restored to Shenzhen", "Shenzhen", buyer.getAddress());
}
}