设计模式(四)——行为型模式

1、命令模式

是一种数据驱动的设计模式，属于行为型模式。请求以命令的形式包裹在对象中，并传给调用对象。调用对象寻找可以处理该明林的适合的对象，并把该命令传给相应的对象，该对象执行命令。

创建一个命令接口

public interface Order {
    void execute();
}

创建一个请求类

public class Stock {
    private String name="ABC";
    private int quantity=10;

    public void buy(){
        System.out.println("Stock [ Name: "+name+", Quantity: " + quantity +" ] bought");
    }
    public void sell(){
        System.out.println("Stock [ Name: "+name+", Quantity: " + quantity +" ] sold");
    }
}

创建接口的实现实体类

public class BuyStock implements Order {
    private Stock stock;

    public BuyStock(Stock stock) {
        this.stock = stock;
    }

    @Override
    public void execute() {
        stock.buy();
    }
}

public class SellStock implements Order {
    private Stock stock;

    public SellStock(Stock stock) {
        this.stock = stock;
    }

    @Override
    public void execute() {
        stock.sell();
    }
}

创建命令调用类

public class Broker {
    private List<Order> orderList = new ArrayList<Order>();

    public void takeOrder(Order order){
        orderList.add(order);
    }
    public void placeOrder(){
        for (Order order : orderList) {
            order.execute();
        }
        orderList.clear();
    }

}

使用命令调用类来接受并执行命令

public class Main {
    public static void main(String[] args) {
        Stock stock = new Stock();
        BuyStock buyStock = new BuyStock(stock);
        SellStock sellStock = new SellStock(stock);
        Broker broker = new Broker();
        broker.takeOrder(buyStock);
        broker.takeOrder(sellStock);
        broker.placeOrder();
    }
}

2、中介者模式

用来降低多个类和对象之间的通信复杂性，处理多个类之间的通信，支持松耦合。

创建中介类

public class ChatRoom {
    public static void showMessage(User user,String message) {
        System.out.println(new Date().toString()+" ["+user.getName()+"] : "+message);
    }
}

创建实体类

public class User {
    private String name;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void showMessage(String message){
        ChatRoom.showMessage(this,message);
    }
}

使用User对象来显示他们之间的通信

public class Main {
    public static void main(String[] args) {
        User rober = new User("Rober");
        User john = new User("john");
        rober.showMessage("Hi,john");
        john.showMessage("Hello rober");
    }
}

3、观察者模式

当对象间存在一对多关系时，使用观察者模式，当一个对象被改变时，所有依赖于他的对象都得到通知并被自动更新，该种模式属于行为模式。

创建Subject类

public class Subject {
    private List<Observer> observerList = new ArrayList<Observer>();
    private int state;

    public int getState() {
        return state;
    }

    public void setState(int state) {
        this.state = state;
        notifyAllObservers();
    }

    public void notifyAllObservers(){
        for (Observer ob:observerList) {
            ob.update();
        }
    }
    public void attach(Observer observer){
        observerList.add(observer);
    }
}

创建observer类

public abstract class Observer {
    private Subject subject;
    public abstract void update();
}

创建实体观察者类

public class BinaryObserver extends Observer{
    private Subject subject;
    public BinaryObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Binary String: "+Integer.toBinaryString(subject.getState()));
    }
}

public class OctalObserver extends Observer{
    private Subject subject;

    public OctalObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Octal String: "+Integer.toOctalString(subject.getState()));
    }
}

使用实体观察者对象

public class Main {
    public static void main(String[] args) {
        Subject subject = new Subject();

        new OctalObserver(subject);
        new BinaryObserver(subject);

        System.out.println("First state change: 15");
        subject.setState(15);
        System.out.println("Second state change: 10");
        subject.setState(10);
    }
}

4、状态模式

在状态模式中，类的行为是基于它的状态改变的，允许对象在内部状态发生改变时改变他的行为。

创建接口及其实现类

public interface State {
    public void doAction(Context context);
}

public class StartState implements State{

    @Override
    public void doAction(Context context) {
        System.out.println("Player is in  start state");
        context.setState(this);
    }

    @Override
    public String toString() {
        return "Start State";
    }
}

public class StopState  implements State{
    @Override
    public void doAction(Context context) {
        System.out.println("Player is in stop state.");
        context.setState(this);
    }

    @Override
    public String toString() {
        return "Stop State";
    }
}

创建context类

public class Context {
    private State state;

    public Context() {
        state = null;
    }

    public State getState() {
        return state;
    }

    public void setState(State state) {
        this.state = state;
    }
}

使用context类查看当状态state改变时的行为变化

public class Main {
    public static void main(String[] args) {
        Context context = new Context();
        State startState = new StartState();
        startState.doAction(context);
        System.out.println(context.getState().toString());

        State stopState = new StopState();
        stopState.doAction(context);
        System.out.println(context.getState().toString());

    }
}

5、策略模式

一个类的行为或算法可以在运行时被更改。这种类型的设计模式属于行为模式。

创建一个接口及其实现类

public interface Strategy {
    public int doOperation(int num1,int num2);
}

public class OperationAdd implements Strategy{
    @Override
    public int doOperation(int num1, int num2) {
        return num1+num2;
    }
}

public class OperationSubstract implements Strategy {
    @Override
    public int doOperation(int num1, int num2) {
        return num1-num2;
    }
}

public class OperationMultiply implements Strategy {
    @Override
    public int doOperation(int num1, int num2) {
        return num1*num2;
    }
}

创建context对象

public class Context {
    private Strategy strategy;

    public Context(Strategy strategy) {
        this.strategy = strategy;
    }
    public int executeStrategy(int num1, int num2){
        return strategy.doOperation(num1,num2);
    }
}

使用context来查看当它改变策略strategy时的行为变化

public class Main {
    public static void main(String[] args) {
        Context context = new Context(new OperationAdd());
        System.out.println("10+5="+context.executeStrategy(3,5));
        context = new Context(new OperationSubstract());
        System.out.println("5-19="+context.executeStrategy(5,19));
        context = new Context(new OperationMultiply());
        System.out.println("4*4="+context.executeStrategy(4,4));
    }
}