设计模式：备忘录模式
什么是备忘录模式
备忘录模式(Memento Pattern)：在不破坏封装的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态，这样可以在以后将对象恢复到原先保存的状态。它是一种对象行为型模式，其别名为Token。
备忘录模式的结构
-
Originator（原发器）
-
Memento（备忘录）
-
MementoCaretaker（负责人）
一个实例
一个画图应用需要每次定位座标位置（Position）.
实例代码
Position
public class Position {
private int x;
private int y;
public Position(int x, int y){
this.x = x;
this.y = y;
}
public Memento save(){
return new Memento(x,y);
}
public void restore(Memento m){
this.x = m.getX();
this.y = m.getY();
}
public int getX() {
return x;
}
public void setX(int x) {
this.x = x;
}
public int getY() {
return y;
}
public void setY(int y) {
this.y = y;
}
public String toString(){
return "x:" + x + ",y:" + y;
}
class Memento {
private int x;
private int y;
public Memento(int x,int y){
this.x = x;
this.y = y;
}
public int getX() {
return x;
}
public void setX(int x) {
this.x = x;
}
public int getY() {
return y;
}
public void setY(int y) {
this.y = y;
}
}
}
MementoCaretaker
import java.util.ArrayList;
import java.util.List;
public class MementoCaretaker {
private List<Position.Memento> mementos = new ArrayList<Position.Memento>();
public Position.Memento getMemento(int i) {
return mementos.get(i);
}
public void setMemento(Position.Memento memento) {
mementos.add(memento);
}
}
Client
public class Client {
private static MementoCaretaker caretaker = new MementoCaretaker();
private static int index = -1;
public static void main(String[] args){
Position pos = new Position(1,2);
draw(pos);
pos.setX(3);
draw(pos);
undo(pos,index);
redo(pos,index);
}
public static void draw(Position position){
caretaker.setMemento(position.save());
index++;
System.out.println("draw! now(" + position + ")");
}
public static void undo(Position position,int i){
position.restore(caretaker.getMemento(i-1));
index--;
System.out.println("undo! now(" + position + ")");
}
public static void redo(Position position,int i){
position.restore(caretaker.getMemento(i+1));
index++;
System.out.println("redo! now(" + position + ")");
}
}
实例结果
draw! now(x:1,y:2)
draw! now(x:3,y:2)
undo! now(x:1,y:2)
redo! now(x:3,y:2)
（完）