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保存对象的某个状态并可以恢复到该状态
例子很多，如回退 ctri + z，回滚，ps恢复到操作历史的某一刻等等。。。
备忘录角色：存储状态
发起人角色：创建备忘录，并利用备忘录存储自己的状态
负责人：管理备忘录
客户端
例子描述：显示一个对象的历史状态
备忘录角色：存储发起人的状态
package dp.memento;public class Memento { private String state; private float x; private float y; public Memento(String state, float x, float y) { this.state = state; this.x = x; this.y = y; } /** * getState. * @return the state */ public String getState() { return state; } /** * setState. * @param state the state to set */ public void setState(String state) { this.state = state; } /** * getX. * @return the x */ public float getX() { return x; } /** * setX. * @param x the x to set */ public void setX(float x) { this.x = x; } /** * getY. * @return the y */ public float getY() { return y; } /** * setY. * @param y the y to set */ public void setY(float y) { this.y = y; }} 发起人角色，希望存储自己的历史状态
package dp.memento;public class Originator { private String state; private float x; private float y; public String getState() { return state; } public void setState(String state) { this.state = state; } public Memento saveToMemento() { return new Memento(state, x, y); } public void restoreFromMemento(Memento memento) { this.state = memento.getState(); this.x = memento.getX(); this.y = memento.getY(); } /** * getX. * @return the x */ public float getX() { return x; } /** * setX. * @param x the x to set */ public void setX(float x) { this.x = x; } /** * getY. * @return the y */ public float getY() { return y; } /** * setY. * @param y the y to set */ public void setY(float y) { this.y = y; }} 备忘录管理者（保存发起人的历史状态记录）
package dp.memento;public class Originator { private String state; private float x; private float y; public String getState() { return state; } public void setState(String state) { this.state = state; } public Memento saveToMemento() { return new Memento(state, x, y); } public void restoreFromMemento(Memento memento) { this.state = memento.getState(); this.x = memento.getX(); this.y = memento.getY(); } /** * getX. * @return the x */ public float getX() { return x; } /** * setX. * @param x the x to set */ public void setX(float x) { this.x = x; } /** * getY. * @return the y */ public float getY() { return y; } /** * setY. * @param y the y to set */ public void setY(float y) { this.y = y; }} 客户端Main
package dp.memento;public class Main { public static void main(String[] args) { Originator originator = new Originator(); //发起人 MementoMgt mementoMgt = new MementoMgt(); //备忘录管理，负责存储历史状态 originator.setState("2017-01-01"); originator.setX(1.4f); originator.setY(5.4f); mementoMgt.add(originator.saveToMemento()); //记录状态 originator.setState("2017-04-03"); originator.setX(44.4f); originator.setY(52.4f); mementoMgt.add(originator.saveToMemento()); //记录状态 originator.setState("2017-06-01"); originator.setX(231.4f); originator.setY(555.4f); mementoMgt.add(originator.saveToMemento()); //记录状态 originator.setState("2017-06-22"); originator.setX(132.4f); originator.setY(53.4f); mementoMgt.add(originator.saveToMemento()); //记录状态 System.out.println("状态历史："); for (Memento m : mementoMgt.getMementoList()) { System.out.println(m.getState() + ": " + m.getX() + ", " + m.getY()); } System.out.println("当前状态："); System.out.println(originator.getState() + ": " + originator.getX() + ", " + originator.getY()); originator.restoreFromMemento(mementoMgt.getByState("2017-04-03")); //恢复到指定状态--2017-04-03 System.out.println("恢复后的状态："); System.out.println(originator.getState() + ": " + originator.getX() + ", " + originator.getY()); }} 结果打印：
本文转自风一样的码农博客园博客，原文链接：http://www.cnblogs.com/chenpi/p/5222287.html，如需转载请自行联系原作者