class Memento {
    private String state;
    public Memento(String state) {
        this.state = state;
    }

    public String GetState() {
        return state;
    }
}

class Originator {
    private String state;

    public void SetState(String state) {
        this.state = state;
    }
    public String GetState() {
        return state;
    }

    public Memento CreateMemento() {
        return (new Memento(state));
    }

    public void SetMemento(Memento memento) {
        state = memento.GetState();
    }

    public void Show() {
        System.out.println("State = " + state);
    }
}

class Caretaker {
    private Memento memento;

    public void SetMemento(Memento memento) {
        this.memento = memento;
    }
    public Memento GetMemento() {
        return memento;
    }
}

public class MementoPattern {
    public static void main(String[] args) {
        Originator o = new Originator();
        o.SetState("ON");
        o.Show();

        Caretaker c = new Caretaker();
        c.SetMemento(o.CreateMemento());

        o.SetState("OFF");
        o.Show();

        o.SetMemento(c.GetMemento());
        o.Show();
    }
}

// 原发器中包含了一些可能会随时间变化的重要数据。它还定义了在备忘录中保存
// 自身状态的方法，以及从备忘录中恢复状态的方法。
class Editor is
    private field text, curX, curY, selectionWidth

    method setText(text) is
        this.text = text

    method setCursor(x, y) is
        this.curX = curX
        this.curY = curY

    method setSelectionWidth(width) is
        this.selectionWidth = width

    // 在备忘录中保存当前的状态。
    method createSnapshot():Snapshot is
        // 备忘录是不可变的对象；因此原发器会将自身状态作为参数传递给备忘
        // 录的构造函数。
        return new Snapshot(this, text, curX, curY, selectionWidth)

// 备忘录类保存有编辑器的过往状态。
class Snapshot is
    private field editor: Editor
    private field text, curX, curY, selectionWidth

    constructor Snapshot(editor, text, curX, curY, selectionWidth) is
        this.editor = editor
        this.text = text
        this.curX = curX
        this.curY = curY
        this.selectionWidth = selectionWidth

    // 在某一时刻，编辑器之前的状态可以使用备忘录对象来恢复。
    method restore() is
        editor.setText(text)
        editor.setCursor(curX, curY)
        editor.setSelectionWidth(selectionWidth)

// 命令对象可作为负责人。在这种情况下，命令会在修改原发器状态之前获取一个
// 备忘录。当需要撤销时，它会从备忘录中恢复原发器的状态。
class Command is
    private field backup: Snapshot

    method makeBackup() is
        backup = editor.createSnapshot()

    method undo() is
        if (backup != null)
            backup.restore()
    // ...

abstract class Handler {
    protected Handler successor;
    public void SetSuccesssor(Handler successor) {
        this.successor = successor;
    }

    public abstract void HandlerRequest(int request);
}

class ConcreteHandler1 extends Handler {
    @Override
    public void HandlerRequest(int request) {
        if (request >= 0 && request < 10) {
            System.out.println("ConcreteHandler1 处理请求 " + request);
        } else if (null != successor) {
            successor.HandlerRequest(request);
        }
    }
}

class ConcreteHandler2 extends Handler {
    @Override
    public void HandlerRequest(int request) {
        if (request >= 10 && request < 20) {
            System.out.println("ConcreteHandler2 处理请求 " + request);
        } else if (null != successor) {
            successor.HandlerRequest(request);
        }
    }
}

class ConcreteHandler3 extends Handler {
    @Override
    public void HandlerRequest(int request) {
        if (request >= 20 && request < 30) {
            System.out.println("ConcreteHandler3 处理请求 " + request);
        } else if (null != successor) {
            successor.HandlerRequest(request);
        }
    }
}

public class ChainOfResponsibilityPattern {
    public static void main(String[] args) {
        Handler h1 = new ConcreteHandler1();
        Handler h2 = new ConcreteHandler2();
        Handler h3 = new ConcreteHandler3();
        h1.SetSuccesssor(h2);
        h2.SetSuccesssor(h3);

        int[] requests = {2, 29, 9, 15, 4, 19};
        for (int i : requests) {
            h1.HandlerRequest(i);
        }
    }
}

// 处理者接口声明了一个创建处理者链的方法。还声明了一个执行请求的方法。
interface ComponentWithContextualHelp is
    method showHelp()


// 简单组件的基础类。
abstract class Component implements ComponentWithContextualHelp is
    field tooltipText: string

    // 组件容器在处理者链中作为“下一个”链接。
    protected field container: Container

    // 如果组件设定了帮助文字，那它将会显示提示信息。如果组件没有帮助文字
    // 且其容器存在，那它会将调用传递给容器。
    method showHelp() is
        if (tooltipText != null)
            // 显示提示信息。
        else
            container.showHelp()


// 容器可以将简单组件和其他容器作为其子项目。链关系将在这里建立。该类将从
// 其父类处继承 showHelp（显示帮助）的行为。
abstract class Container extends Component is
    protected field children: array of Component

    method add(child) is
        children.add(child)
        child.container = this


// 原始组件应该能够使用帮助操作的默认实现...
class Button extends Component is
    // ...

// 但复杂组件可能会对默认实现进行重写。如果无法以新的方式来提供帮助文字，
// 那组件总是还能调用基础实现的（参见 Component 类）。
class Panel extends Container is
    field modalHelpText: string

    method showHelp() is
        if (modalHelpText != null)
            // 显示包含帮助文字的模态窗口。
        else
            super.showHelp()

// ...同上...
class Dialog extends Container is
    field wikiPageURL: string

    method showHelp() is
        if (wikiPageURL != null)
            // 打开百科帮助页面。
        else
            super.showHelp()


// 客户端代码。
class Application is
    // 每个程序都能以不同方式对链进行配置。
    method createUI() is
        dialog = new Dialog("预算报告")
        dialog.wikiPageURL = "http://..."
        panel = new Panel(0, 0, 400, 800)
        panel.modalHelpText = "本面板用于..."
        ok = new Button(250, 760, 50, 20, "确认")
        ok.tooltipText = "这是一个确认按钮..."
        cancel = new Button(320, 760, 50, 20, "取消")
        // ...
        panel.add(ok)
        panel.add(cancel)
        dialog.add(panel)

    // 想象这里会发生什么。
    method onF1KeyPress() is
        component = this.getComponentAtMouseCoords()
        component.showHelp()

abstract class Mediator {
    public abstract void Send(String message, Colleague colleague);
}

class ConcreteMediator extends Mediator {
    private ConcreteColleague1 colleague1;
    private ConcreteColleague2 colleague2;

    public void setColleague1(ConcreteColleague1 colleague1) {
        this.colleague1 = colleague1;
    }

    public void setColleague2(ConcreteColleague2 colleague2) {
        this.colleague2 = colleague2;
    }

    @Override
    public void Send(String message, Colleague colleague) {
        if (colleague == colleague1) {
            colleague2.Notify(message);
        } else if (colleague == colleague2){
            colleague1.Notify(message);
        } else {
            System.out.println("Error!");
        }
    }
}

abstract class Colleague {
    protected Mediator mediator;

    public Colleague(Mediator mediator) {
        this.mediator = mediator;
    }

    public void Send(String message) {
        mediator.Send(message, this);
    }

    public abstract void Notify(String message);
}

class ConcreteColleague1 extends Colleague {
    public ConcreteColleague1(Mediator mediator) {
        super(mediator);
    }

    @Override
    public void Notify(String message) {
        System.out.println("同事1得到信息：" + message);
    }
}

class ConcreteColleague2 extends Colleague {
    public ConcreteColleague2(Mediator mediator) {
        super(mediator);
    }

    @Override
    public void Notify(String message) {
        System.out.println("同事2得到信息：" + message);
    }
}

public class MediatorPattern {
    public static void main(String[] args) {
        ConcreteMediator mediator = new ConcreteMediator();
        ConcreteColleague1 colleague1 = new ConcreteColleague1(mediator);
        ConcreteColleague2 colleague2 = new ConcreteColleague2(mediator);

        mediator.setColleague1(colleague1);
        mediator.setColleague2(colleague2);

        colleague1.Send("How are you?");
        colleague2.Send("Fine, thank you. And you?");
        colleague1.Send("I'm fine. Thankes.");
    }
}

// 中介者接口声明了一个能让组件将各种事件通知给中介者的方法。中介者可对这
// 些事件做出响应并将执行工作传递给其他组件。
interface Mediator is
    method notify(sender: Component, event: string)


// 具体中介者类可解开各组件之间相互交叉的连接关系并将其转移到中介者中。
class AuthenticationDialog implements Mediator is
    private field title: string
    private field loginOrRegisterChkBx: Checkbox
    private field loginUsername, loginPassword: Textbox
    private field registrationUsername, registrationPassword,
                  registrationEmail: Textbox
    private field okBtn, cancelBtn: Button

    constructor AuthenticationDialog() is
        // 创建所有组件对象并将当前中介者传递给其构造函数以建立连接。

    // 当组件中有事件发生时，它会通知中介者。中介者接收到通知后可自行处理，
    // 也可将请求传递给另一个组件。
    method notify(sender, event) is
        if (sender == loginOrRegisterChkBx and event == "check")
            if (loginOrRegisterChkBx.checked)
                title = "登录"
                // 1. 显示登录表单组件。
                // 2. 隐藏注册表单组件。
            else
                title = "注册"
                // 1. 显示注册表单组件。
                // 2. 隐藏登录表单组件。

        if (sender == okBtn && event == "click")
            if (loginOrRegister.checked)
                // 尝试找到使用登录信息的用户。
                if (!found)
                    // 在登录字段上方显示错误信息。
            else
                // 1. 使用注册字段中的数据创建用户账号。
                // 2. 完成用户登录工作。 …


// 组件会使用中介者接口与中介者进行交互。因此只需将它们与不同的中介者连接
// 起来，你就能在其他情境中使用这些组件了。
class Component is
    field dialog: Mediator

    constructor Component(dialog) is
        this.dialog = dialog

    method click() is
        dialog.notify(this, "click")

    method keypress() is
        dialog.notify(this, "keypress")

// 具体组件之间无法进行交流。它们只有一个交流渠道，那就是向中介者发送通知。
class Button extends Component is
    // ...

class Textbox extends Component is
    // ...

class Checkbox extends Component is
    method check() is
        dialog.notify(this, "check")
    // ...

class Context {
    private String input;
    private String output;

    public void setInput(String input) {
        this.input = input;
    }

    public String getInput() {
        return this.input;
    }

    public void setOutput(String output) {
        this.output = output;
    }

    public String getOutput() {
        return this.output;
    }
}

abstract class AbstractExpression {
    public abstract void Interpret(Context context);
}

class TerminalExpression extends AbstractExpression {
    @Override
    public void Interpret(Context context) {
        context.setOutput("终端" + context.getInput());
        System.out.println(context.getInput() + "经过终端解释器解释为：" + context.getOutput());
    }
}

class NonterminalExpression extends AbstractExpression {
    @Override
    public void Interpret(Context context) {
        context.setOutput("非终端" + context.getInput());
        System.out.println(context.getInput() + "经过非终端解释器解释为：" + context.getOutput());
    }
}

public class InterpreterPattern {
    public static void main(String[] args) {
        Context context = new Context();
        context.setInput("ABC");

        AbstractExpression expression1 = new TerminalExpression();
        expression1.Interpret(context);

        AbstractExpression expression2 = new NonterminalExpression();
        expression2.Interpret(context);
    }
}

abstract class Subject {
    protected String name;
    protected String state;
    protected List<Observer> observers = new ArrayList<Observer>();

    public abstract String getState();
    public abstract void setState(String state);
    public abstract void Notify();

    public Subject(String name) {
        this.name = name;
    }

    public void Attach(Observer observer) {
        observers.add(observer);
    }

    public void Detach(Observer observer) {
        observers.remove(observer);
    }
}

abstract class Observer {
    protected String name;
    protected Subject subject;
    public Observer(String name, Subject subject) {
        this.name = name;
        this.subject = subject;
    }
    public abstract void Update();
}

class ConcreteSubject extends Subject {
    public ConcreteSubject(String name) {
        super(name);
    }

    @Override
    public String getState() {
        return state;
    }

    @Override
    public void setState(String state) {
        this.state = state;
    }

    @Override
    public void Notify() {
        System.out.println("======= " + this.name + "主题发布新消息 =======");
        for (Observer observer : observers) {
            observer.Update();
        }
    }
}

class ConcreteObserver extends Observer {
    private String state;
    public ConcreteObserver(String name, Subject subject) {
        super(name, subject);
    }

    @Override
    public void Update() {
        state = subject.getState();
        System.out.println(this.name + "收到当前状态：" + state);
    }
}

public class ObserverPattern {
    public static void main(String[] args) {
        ConcreteSubject subject = new ConcreteSubject("天气");
        ConcreteObserver observer1 = new ConcreteObserver("张三", subject);
        ConcreteObserver observer2 = new ConcreteObserver("李四", subject);
        ConcreteObserver observer3 = new ConcreteObserver("王五", subject);

        subject.Attach(observer1);
        subject.Attach(observer2);
        subject.Attach(observer3);
        subject.setState("今天下雨");
        subject.Notify();

        subject.Detach(observer2);
        subject.setState("明天天晴");
        subject.Notify();
    }
}

// 发布者基类包含订阅管理代码和通知方法。
class EventManager is
    private field listeners: hash map of event types and listeners

    method subscribe(eventType, listener) is
        listeners.add(eventType, listener)

    method unsubscribe(eventType, listener) is
        listeners.remove(eventType, listener)

    method notify(eventType, data) is
        foreach (listener in listeners.of(eventType)) do
            listener.update(data)

// 具体发布者包含一些订阅者感兴趣的实际业务逻辑。我们可以从发布者基类中扩
// 展出该类，但在实际情况下并不总能做到，因为具体发布者可能已经是子类了。
// 在这种情况下，你可用组合来修补订阅逻辑，就像我们在这里做的一样。
class Editor is
    public field events: EventManager
    private field file: File

    constructor Editor() is
        events = new EventManager()

    // 业务逻辑的方法可将变化通知给订阅者。
    method openFile(path) is
        this.file = new File(path)
        events.notify("open", file.name)

    method saveFile() is
        file.write()
        events.notify("save", file.name)

    // ...


// 这里是订阅者接口。如果你的编程语言支持函数类型，则可用一组函数来代替整
// 个订阅者的层次结构。
interface EventListener is
    method update(filename)

// 具体订阅者会对其注册的发布者所发出的更新消息做出响应。
class LoggingListener implements EventListener is
    private field log: File
    private field message

    constructor LoggingListener(log_filename, message) is
        this.log = new File(log_filename)
        this.message = message

    method update(filename) is
        log.write(replace('%s',filename,message))

class EmailAlertsListener implements EventListener is
    private field email: string

    constructor EmailAlertsListener(email, message) is
        this.email = email
        this.message = message

    method update(filename) is
        system.email(email, replace('%s',filename,message))


// 应用程序可在运行时配置发布者和订阅者。
class Application is
    method config() is
        editor = new Editor()

        logger = new LoggingListener(
            "/path/to/log.txt",
            "有人打开了文件：%s");
        editor.events.subscribe("open", logger)

        emailAlerts = new EmailAlertsListener(
            "admin@example.com",
            "有人更改了文件：%s")
        editor.events.subscribe("save", emailAlerts)

abstract class Command {
    protected Receiver receiver;
    public Command(Receiver receiver) {
        this.receiver = receiver;
    }

    public abstract void Execute();
}

class ConcreteCommand extends Command {
    public ConcreteCommand(Receiver receiver) {
        super(receiver);
    }

    @Override
    public void Execute() {
        receiver.Action();
    }
}

class Invoker {
    private Command command;

    public Invoker(Command command) {
        this.command = command;
    }

    public void ExecuteCommand() {
        command.Execute();
    }
}

class Receiver {
    public void Action() {
        System.out.println("执行请求");
    }
}

public class CommandPattern {
    public static void main(String[] args) {
        Receiver receiver = new Receiver();
        Command cmd = new ConcreteCommand(receiver);
        Invoker invoker = new Invoker(cmd);
        invoker.ExecuteCommand();
    }
}

// 命令基类会为所有具体命令定义通用接口。
abstract class Command is
    protected field app: Application
    protected field editor: Editor
    protected field backup: text

    constructor Command(app: Application, editor: Editor) is
        this.app = app
        this.editor = editor

    // 备份编辑器状态。
    method saveBackup() is
        backup = editor.text

    // 恢复编辑器状态。
    method undo() is
        editor.text = backup

    // 执行方法被声明为抽象以强制所有具体命令提供自己的实现。该方法必须根
    // 据命令是否更改编辑器的状态返回 true 或 false。
    abstract method execute()


// 这里是具体命令。
class CopyCommand extends Command is
    // 复制命令不会被保存到历史记录中，因为它没有改变编辑器的状态。
    method execute() is
        app.clipboard = editor.getSelection()
        return false

class CutCommand extends Command is
    // 剪切命令改变了编辑器的状态，因此它必须被保存到历史记录中。只要方法
    // 返回 true，它就会被保存。
    method execute() is
        saveBackup()
        app.clipboard = editor.getSelection()
        editor.deleteSelection()
        return true

class PasteCommand extends Command is
    method execute() is
        saveBackup()
        editor.replaceSelection(app.clipboard)
        return true

// 撤销操作也是一个命令。
class UndoCommand extends Command is
    method execute() is
        app.undo()
        return false


// 全局命令历史记录就是一个堆桟。
class CommandHistory is
    private field history: array of Command

    // 后进...
    method push(c: Command) is
        // 将命令压入历史记录数组的末尾。

    // ...先出
    method pop():Command is
        // 从历史记录中取出最近的命令。


// 编辑器类包含实际的文本编辑操作。它会担任接收者的角色：最后所有命令都会
// 将执行工作委派给编辑器的方法。
class Editor is
    field text: string

    method getSelection() is
        // 返回选中的文字。

    method deleteSelection() is
        // 删除选中的文字。

    method replaceSelection(text) is
        // 在当前位置插入剪贴板中的内容。

// 应用程序类会设置对象之间的关系。它会担任发送者的角色：当需要完成某些工
// 作时，它会创建并执行一个命令对象。
class Application is
    field clipboard: string
    field editors: array of Editors
    field activeEditor: Editor
    field history: CommandHistory

    // 将命令分派给 UI 对象的代码可能会是这样的。
    method createUI() is
        // ...
        copy = function() { executeCommand(
            new CopyCommand(this, activeEditor)) }
        copyButton.setCommand(copy)
        shortcuts.onKeyPress("Ctrl+C", copy)

        cut = function() { executeCommand(
            new CutCommand(this, activeEditor)) }
        cutButton.setCommand(cut)
        shortcuts.onKeyPress("Ctrl+X", cut)

        paste = function() { executeCommand(
            new PasteCommand(this, activeEditor)) }
        pasteButton.setCommand(paste)
        shortcuts.onKeyPress("Ctrl+V", paste)

        undo = function() { executeCommand(
            new UndoCommand(this, activeEditor)) }
        undoButton.setCommand(undo)
        shortcuts.onKeyPress("Ctrl+Z", undo)

    // 执行一个命令并检查它是否需要被添加到历史记录中。
    method executeCommand(command) is
        if (command.execute)
            history.push(command)

    // 从历史记录中取出最近的命令并运行其 undo（撤销）方法。请注意，你并
    // 不知晓该命令所属的类。但是我们不需要知晓，因为命令自己知道如何撤销
    // 其动作。
    method undo() is
        command = history.pop()
        if (command != null)
            command.undo()

interface Iterator {
    public Object first();
    public Object next();
    public boolean isDone();
    public Object currentItem();
}

class ConcreteIterator implements Iterator {
    private int current = 0;
    private ConcreteAggregate aggregate;

    public ConcreteIterator(ConcreteAggregate aggregate) {
        this.aggregate = aggregate;
    }

    @Override
    public Object first() {
        return aggregate.get(0);
    }

    @Override
    public Object next() {
        current++;
        if (current < aggregate.size()) {
            return aggregate.get(current);
        }
        return null;
    }

    @Override
    public boolean isDone() {
        return (current >= aggregate.size()) ? true : false;
    }

    @Override
    public Object currentItem() {
        return aggregate.get(current);
    }
}

interface Aggregate {
    public Iterator CreateIterator();
}

class ConcreteAggregate implements Aggregate {
    private List<Object> items = new ArrayList<Object>();

    @Override
    public Iterator CreateIterator() {
        return new ConcreteIterator(this);
    }

    public int size() {
        return items.size();
    }

    public Object get(int index) {
        return items.get(index);
    }

    public void set(int index, Object element) {
        items.set(index, element);
    }

    public void add(Object element) {
        items.add(element);
    }
}

public class IteratorPattern {
    public static void main(String[] args) {
        ConcreteAggregate aggregate = new ConcreteAggregate();
        aggregate.add("张三");
        aggregate.add("李四");
        aggregate.add("王五");
        aggregate.add("赵六");

        Iterator iter = new ConcreteIterator(aggregate);
        Object item = iter.first();
        System.out.println("第一个人是：" + item);
        System.out.println("所有人的名单是：");
        while (!iter.isDone()) {
            System.out.println(iter.currentItem());
            iter.next();
        }
    }
}

// 集合接口必须声明一个用于生成迭代器的工厂方法。如果程序中有不同类型的迭
// 代器，你也可以声明多个方法。
interface SocialNetwork is
    method createFriendsIterator(profileId):ProfileIterator
    method createCoworkersIterator(profileId):ProfileIterator


// 每个具体集合都与其返回的一组具体迭代器相耦合。但客户并不是这样的，因为
// 这些方法的签名将会返回迭代器接口。
class WeChat implements SocialNetwork is
    // ...大量的集合代码应该放在这里...

    // 迭代器创建代码。
    method createFriendsIterator(profileId) is
        return new WeChatIterator(this, profileId, "friends")
    method createCoworkersIterator(profileId) is
        return new WeChatIterator(this, profileId, "coworkers")


// 所有迭代器的通用接口。
interface ProfileIterator is
    method getNext():Profile
    method hasMore():bool


// 具体迭代器类。
class WeChatIterator implements ProfileIterator is
    // 迭代器需要一个指向其遍历集合的引用。
    private field weChat: WeChat
    private field profileId, type: string

    // 迭代器对象会独立于其他迭代器来对集合进行遍历。因此它必须保存迭代器
    // 的状态。
    private field currentPosition
    private field cache: array of Profile

    constructor WeChatIterator(weChat, profileId, type) is
        this.weChat = weChat
        this.profileId = profileId
        this.type = type

    private method lazyInit() is
        if (cache == null)
            cache = weChat.socialGraphRequest(profileId, type)

    // 每个具体迭代器类都会自行实现通用迭代器接口。
    method getNext() is
        if (hasMore())
            currentPosition++
            return cache[currentPosition]

    method hasMore() is
        lazyInit()
        return currentPosition < cache.length


// 这里还有一个有用的绝招：你可将迭代器传递给客户端类，无需让其拥有访问整
// 个集合的权限。这样一来，你就无需将集合暴露给客户端了。
//
// 还有另一个好处：你可在运行时将不同的迭代器传递给客户端，从而改变客户端
// 与集合互动的方式。这一方法可行的原因是客户端代码并没有和具体迭代器类相
// 耦合。
class SocialSpammer is
    method send(iterator: ProfileIterator, message: string) is
        while (iterator.hasMore())
            profile = iterator.getNext()
            System.sendEmail(profile.getEmail(), message)


// 应用程序（Application）类可对集合和迭代器进行配置，然后将其传递给客户
// 端代码。
class Application is
    field network: SocialNetwork
    field spammer: SocialSpammer

    method config() is
        if working with WeChat
            this.network = new WeChat()
        if working with LinkedIn
            this.network = new LinkedIn()
        this.spammer = new SocialSpammer()

    method sendSpamToFriends(profile) is
        iterator = network.createFriendsIterator(profile.getId())
        spammer.send(iterator, "非常重要的消息")

    method sendSpamToCoworkers(profile) is
        iterator = network.createCoworkersIterator(profile.getId())
        spammer.send(iterator, "非常重要的消息")

class Class1 {
    public void op1() {
        System.out.println("方法1");
    }
}

class Class2 {
    public void op2() {
        System.out.println("方法2");
    }
}

class Class3 {
    public void op3() {
        System.out.println("方法3");
    }
}

class Facade {
    private Class1 one = new Class1();
    private Class2 two = new Class2();
    private Class3 three = new Class3();

    public void op1() {
        System.out.println("Facade op1()");
        one.op1();
    }

    public void op2() {
        System.out.println("Facade op2()");
        two.op2();
    }

    public void op3() {
        System.out.println("Facade op3()");
        three.op3();
    }

    public void Method() {
        System.out.println("Facade Method()");
        three.op3();
        two.op2();
        one.op1();
    }
}

public class FacadePattern {
    public static void main(String[] args) {
        Facade facade = new Facade();
        facade.Method();

        facade.op1();
    }
}

// 这里有复杂第三方视频转换框架中的一些类。我们不知晓其中的代码，因此无法
// 对其进行简化。

class VideoFile
// ...

class OggCompressionCodec
// ...

class MPEG4CompressionCodec
// ...

class CodecFactory
// ...

class BitrateReader
// ...

class AudioMixer
// ...


// 为了将框架的复杂性隐藏在一个简单接口背后，我们创建了一个外观类。它是在
// 功能性和简洁性之间做出的权衡。
class VideoConverter is
    method convert(filename, format):File is
        file = new VideoFile(filename)
        sourceCodec = new CodecFactory.extract(file)
        if (format == "mp4")
            destinationCodec = new MPEG4CompressionCodec()
        else
            destinationCodec = new OggCompressionCodec()
        buffer = BitrateReader.read(filename, sourceCodec)
        result = BitrateReader.convert(buffer, destinationCodec)
        result = (new AudioMixer()).fix(result)
        return new File(result)

// 应用程序的类并不依赖于复杂框架中成千上万的类。同样，如果你决定更换框架，
// 那只需重写外观类即可。
class Application is
    method main() is
        convertor = new VideoConverter()
        mp4 = convertor.convert("funny-cats-video.ogg", "mp4")
        mp4.save()

abstract class Subject {
    public abstract void Request();
}

class RealSubject extends Subject {
    @Override
    public void Request() {
        System.out.println("真实的请求");
    }
}

class Proxy extends Subject {
    private RealSubject real;

    @Override
    public void Request() {
        if (null == real) {
            real = new RealSubject();
        }
        real.Request();
    }
}

// 远程服务接口。
interface ThirdPartyTVLib is
    method listVideos()
    method getVideoInfo(id)
    method downloadVideo(id)

// 服务连接器的具体实现。该类的方法可以向腾讯视频请求信息。请求速度取决于
// 用户和腾讯视频的互联网连接情况。如果同时发送大量请求，即使所请求的信息
// 一模一样，程序的速度依然会减慢。
class ThirdPartyTVClass implements ThirdPartyTVLib is
    method listVideos() is
        // 向腾讯视频发送一个 API 请求。

    method getVideoInfo(id) is
        // 获取某个视频的元数据。

    method downloadVideo(id) is
        // 从腾讯视频下载一个视频文件。

// 为了节省网络带宽，我们可以将请求结果缓存下来并保存一段时间。但你可能无
// 法直接将这些代码放入服务类中。比如该类可能是第三方程序库的一部分或其签
// 名是`final（最终）`。因此我们会在一个实现了服务类接口的新代理类中放入
// 缓存代码。当代理类接收到真实请求后，才会将其委派给服务对象。
class CachedTVClass implements ThirdPartyTVLib is
    private field service: ThirdPartyTVLib
    private field listCache, videoCache
    field needReset

    constructor CachedTVClass(service: ThirdPartyTVLib) is
        this.service = service

    method listVideos() is
        if (listCache == null || needReset)
            listCache = service.listVideos()
        return listCache

    method getVideoInfo(id) is
        if (videoCache == null || needReset)
            videoCache = service.getVideoInfo(id)
        return videoCache

    method downloadVideo(id) is
        if (!downloadExists(id) || needReset)
            service.downloadVideo(id)

// 之前直接与服务对象交互的 GUI 类不需要改变，前提是它仅通过接口与服务对
// 象交互。我们可以安全地传递一个代理对象来代替真实服务对象，因为它们都实
// 现了相同的接口。
class TVManager is
    protected field service: ThirdPartyTVLib

    constructor TVManager(service: ThirdPartyTVLib) is
        this.service = service

    method renderVideoPage(id) is
        info = service.getVideoInfo(id)
        // 渲染视频页面。

    method renderListPanel() is
        list = service.listVideos()
        // 渲染视频缩略图列表。

    method reactOnUserInput() is
        renderVideoPage()
        renderListPanel()

// 程序可在运行时对代理进行配置。
class Application is
    method init() is
        aTVService = new ThirdPartyTVClass()
        aTVProxy = new CachedTVClass(aTVService)
        manager = new TVManager(aTVProxy)
        manager.reactOnUserInput()