设计模式-备忘录模式

1.需要的类

一个备忘录类：用来set，get属性
一个记录者类：操作备忘录里的属性，以及创建备忘录
一个管理员类：通过记录者创建备忘录，并将其记录

2.实现代码

属性类（备忘录里的属性）

/*** 目标类，存储商品金额和变更时间*/
public class CashFile {//商品金额private double money;//变更时间private Date date;public CashFile(double money, Date date) {this.money = money;this.date = date;}public double getMoney() {return money;}public void setMoney(double money) {this.money = money;}public Date getDate() {return date;}public void setDate(Date date) {this.date = date;}}

备忘录类

/*** 备忘录类*/
public class CashMemento {private CashFile cashFile;public CashMemento(CashFile cashFile){this.cashFile = cashFile;}public CashFile getCashFile(){return cashFile;}public void setCashFile(CashFile cashFile){this.cashFile = cashFile;}
}

记录者类

/*** 记录者类*/
public class CashOriginator {private CashFile cashFile;public CashFile getCashFile() {return cashFile;}public void setCashFile(CashFile cashFile) {this.cashFile = cashFile;}public CashMemento createMemento() {return new CashMemento(cashFile);}public void restoreMemento(CashMemento cashMemento) {this.cashFile = cashMemento.getCashFile();}
}

管理员类

/*** 管理员*/
public class Admin {private int cursorIndex;private List<CashMemento> cashMementoList = new ArrayList<>();public void append(CashMemento cashMemento){cashMementoList.add(cashMemento);cursorIndex++;}public CashMemento undo(){if(cursorIndex > 0){cursorIndex--;return cashMementoList.get(cursorIndex);}return cashMementoList.get(0);}public CashMemento redo(){if(cursorIndex < cashMementoList.size()-1){cursorIndex++;return cashMementoList.get(cursorIndex);}return cashMementoList.get(cashMementoList.size()-1);}
}

使用

@SpringBootApplication
public class MemoApplication {public static void main(String[] args) {Admin admin = new Admin();CashOriginator originator = new CashOriginator();originator.setCashFile(new CashFile(500,new Date()));admin.append(originator.createMemento());originator.setCashFile(new CashFile(400,new Date()));admin.append(originator.createMemento());originator.setCashFile(new CashFile(300,new Date()));admin.append(originator.createMemento());System.out.println(admin.undo().getCashFile().getMoney());System.out.println(admin.undo().getCashFile().getMoney());System.out.println(admin.undo().getCashFile().getMoney());System.out.println(admin.redo().getCashFile().getMoney());}}