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，这样以后就可以将该对象恢复到先前保存的状态。

栗子

/**
 * 备忘录(保存需要存储的数据)
 */
public class Memoto {

    private String musicName;
    private double percent;

    public String getMusicName() {
        return musicName;
    }

    public void setMusicName(String musicName) {
        this.musicName = musicName;
    }

    public double getPercent() {
        return percent;
    }

    public void setPercent(double percent) {
        this.percent = percent;
    }
}

/**
 * 备忘录管理类
 */
public class Caretaker {

    private Memoto memoto;

    public Memoto getMemoto() {
        return memoto;
    }

    public void setMemoto(Memoto memoto) {
        this.memoto = memoto;
    }
}

/**
 * 以播放音乐为例
 */
public class Music {

    private String musicName;
    private double percent;

    public void play(){
        this.musicName = "十年";
        this.percent = 0.5;
        System.out.println("播放"+musicName+",进度"+percent);
    }

    public void quit() {
        System.out.println("退出播放");
    }

    public Memoto save(){
        System.out.println("保存播放进度");
        Memoto memoto = new Memoto();
        memoto.setMusicName(musicName);
        memoto.setPercent(percent);
        return memoto;
    }

    public void restore(Memoto memoto){
        this.musicName = memoto.getMusicName();
        this.percent = memoto.getPercent();
        System.out.println("恢复播放"+musicName+",进度"+percent);
    }
}

/**
 * 测试类
 */
public class Test {

    public static void main(String[] args) {
        Music music = new Music();
        music.play();
        Caretaker caretaker = new Caretaker();
        caretaker.setMemoto(music.save());
        music.quit();
        music.restore(caretaker.getMemoto());
    }
}