定義
備忘錄模式(Memento Pattern)保存一個(gè)對(duì)象的某個(gè)狀態(tài)襟雷,以便在適當(dāng)?shù)臅r(shí)候恢復(fù)對(duì)象。備忘錄模式屬于行為型模式仁烹。
實(shí)現(xiàn)
備忘錄模式使用三個(gè)類 Memento嗤军、Originator 和 CareTaker。Memento 包含了要被恢復(fù)的對(duì)象的狀態(tài)晃危。Originator 創(chuàng)建并在 Memento 對(duì)象中存儲(chǔ)狀態(tài)。Caretaker 對(duì)象負(fù)責(zé)從 Memento 中恢復(fù)對(duì)象的狀態(tài)老客。
MementoPatternDemo僚饭,我們的演示類使用 CareTaker 和 Originator 對(duì)象來顯示對(duì)象的狀態(tài)恢復(fù)。
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步驟 1
創(chuàng)建 Memento 類胧砰。
Memento.java
public class Memento {
private String state;
public Memento(String state){
this.state = state;
}
public String getState(){
return state;
}
}
步驟 2
創(chuàng)建 Originator 類鳍鸵。
Originator.java
public class Originator {
private String state;
public void setState(String state){
this.state = state;
}
public String getState(){
return state;
}
public Memento saveStateToMemento(){
return new Memento(state);
}
public void getStateFromMemento(Memento Memento){
state = Memento.getState();
}
}
步驟 3
創(chuàng)建 CareTaker 類。
CareTaker.java
import java.util.ArrayList;
import java.util.List;
public class CareTaker {
private List<Memento> mementoList = new ArrayList<Memento>();
public void add(Memento state){
mementoList.add(state);
}
public Memento get(int index){
return mementoList.get(index);
}
}
步驟 4
使用 CareTaker 和 Originator 對(duì)象尉间。
MementoPatternDemo.java
public class MementoPatternDemo {
public static void main(String[] args) {
Originator originator = new Originator();
CareTaker careTaker = new CareTaker();
originator.setState("State #1");
originator.setState("State #2");
careTaker.add(originator.saveStateToMemento());
originator.setState("State #3");
careTaker.add(originator.saveStateToMemento());
originator.setState("State #4");
System.out.println("Current State: " + originator.getState());
originator.getStateFromMemento(careTaker.get(0));
System.out.println("First saved State: " + originator.getState());
originator.getStateFromMemento(careTaker.get(1));
System.out.println("Second saved State: " + originator.getState());
}
}
步驟 5
驗(yàn)證輸出偿乖。
Current State: State #4
First saved State: State #2
Second saved State: State #3