public interface PhoneState {
    void handle(Phone phone);
}
public class NormalState implements PhoneState {
    @Override
    public void handle(Phone phone) {
        System.out.println("系统关机");
        phone.setPhoneState(new ShutdownState());
    }
}
public class ShutdownState implements PhoneState {
    @Override
    public void handle(Phone phone) {
        System.out.println("系统开机");
        phone.setPhoneState(new NormalState());
    }
}
public class Phone {
    private PhoneState phoneState;
    public Phone(){
        this.phoneState=new ShutdownState();
    }
    public void clickButton(){
        phoneState.handle(this);
    }
    public void setPhoneState(PhoneState phoneState) {
        System.out.println("状态改变:"+phoneState.toString());
        this.phoneState = phoneState;
    }
}
public class App {
    public static void main(String[] args) {
        Phone phone=new Phone();
        phone.clickButton();
        phone.clickButton();
    }
}

public class Subject {
    private List<Observer> observers;
    public Subject() {
        observers = new ArrayList<>();
    }
    protected void attach(Observer observer) {
        observers.add(observer);
    }
    protected void detach(Observer observer) {
        observers.remove(observer);
    }
    protected void notify_(Object args) {
        observers.forEach(observer -> observer.update(args));
    }
}
public class VolumeSubject extends Subject {
    private Integer vol;
    public void changeVol(Integer vol){
        this.vol=vol;
        notify_(vol);
    }
}
public interface Observer {
    void update(Object message);
}
public class SpeakerObserver implements Observer {
    public SpeakerObserver(Subject subject){
        subject.attach(this);
    }
    @Override
    public void update(Object vol) {
        System.out.println("扬声器音量调整"+vol);
    }
}
public class VolumeBarObserver implements Observer {
    public VolumeBarObserver(Subject subject){
        subject.attach(this);
    }
    @Override
    public void update(Object vol) {
        System.out.println("音量条显示器调整"+vol);
    }
}
public class App {
    public static void main(String[] args) {
        VolumeSubject subject=new VolumeSubject();
        Observer speaker=new SpeakerObserver(subject);
        Observer volumeBar=new VolumeBarObserver(subject);
        subject.changeVol(4);
        subject.changeVol(5);
        subject.changeVol(6);
    }
}

public class IterOriginator {
    private final Node root;
    private Node cursor = null;
    private Boolean isDone = false;
    private Stack<Node> stack;
    private Memento<Node> memento;
    public IterOriginator(Node root) {
        this.root = root;
        stack = new Stack<>();
        cursor = root;
        stack.push(cursor);
    }
    public Node next() {
        memento = createMemento();
        if (stack.isEmpty()) {
            isDone = true;
            return null;
        }
        Node top = stack.pop();
        cursor = top.right;
        if (cursor != null) {
            stack.push(cursor);
        }
        cursor = top.left;
        if (cursor != null) {
            stack.push(cursor);
        }
        return top;
    }
    public void undo() {
        setMemento(memento);
    }
    public Memento<Node> createMemento() {
        Memento<Node> memento = new Memento<>();
        Stack newStack=(Stack)stack.clone();
        memento.status = newStack;
        return memento;
    }
    public void setMemento(Memento<Node> memento) {
        this.stack = memento.status;
    }
}
public class Memento<T> {
    public Stack<T> status;
}
public class Node {
    public Node left;
    public Node right;
    public String name;
    public Node(Node left, Node right, String name) {
        this.left = left;
        this.right = right;
        this.name = name;
    }
    public Node(String name) {
        this.name = name;
    }
    public IterOriginator createFrontIndexIterator() {
        return new IterOriginator(this);
    }
}
public class App {
    public static void main(String[] args) {
        Node one = new Node(
                new Node(new Node(new Node("8"),null,"3"), new Node(new Node("6"), new Node("7"), "4"), "2"),
                new Node(new Node("9"),null,"5"), "1");
        IterOriginator iterOriginator=one.createFrontIndexIterator();
        Memento first=iterOriginator.createMemento();
        System.out.println(iterOriginator.next().name);
        System.out.println(iterOriginator.next().name);
        iterOriginator.setMemento(first);
        System.out.println(iterOriginator.next().name);
        System.out.println(iterOriginator.next().name);
    }
}