JAVA设计模式---观察者模式

观察者模式定义了对象之间的一对多依赖，这样一来，当一个对象改变状态时，它的所有的依赖者都会收到通知并自动更新，提供了一种对象设计，让主题和观察者之间松耦合，实现代码如下：

1、主题部分：

　　定义主题接口：

public interface Subject {
    /*增加观察者*/
    public void addObserver(Observer Observer);

    /*删除观察者*/
    public void delObserver(Observer Observer);

    /*通知所的观察者*/
    public void notifyObserver();

    /*自身的操作*/
    public void operation();
}

　　主题实现：

public class SubSubject implements Subject{
    private List<Observer> observers;
    private float temp;
    private float humidity;
    private float pressure;

    public SubSubject() {
        observers = new ArrayList<Observer>();
    }

    @Override
    public void addObserver(Observer Observer) {
        observers.add(Observer);
    }

    @Override
    public void delObserver(Observer Observer) {
        int i = observers.indexOf(observers);
        if(i>=0){
            observers.remove(i);
        }
    }

    @Override
    public void notifyObserver() {
        for(int i=0;i<observers.size();i++){
            Observer observer = observers.get(i);
            observer.update(temp,humidity,pressure);
        }
    }

    @Override
    public void operation() {
        notifyObserver();
    }

    public void setParameters(float temp,float humidity,float pressure){
        this.temp = temp;
        this.humidity = humidity;
        this.pressure = pressure;
        operation();
    }
}

　　2、观察者部分：

　　定义观察者接口：

public interface Observer {
    public void update(float temp,float humidity,float pressure);
}

　　定义展示元素接口：

public interface DisplayElement {
    public void display();
}

　　观察者1实现：

public class Observer1 implements Observer,DisplayElement {
    private float temp;
    private float humidity;
    private float pressure;
    private SubSubject mySubject1;

    /*保存对Subject的引用，以后如果想取消注册，可以用到*/
    public Observer1(SubSubject mySubject1) {
        this.mySubject1 = mySubject1;
        mySubject1.addObserver(this);
    }

    @Override
    public void update(float temp, float humidity, float pressure) {
        this.temp = temp;
        this.humidity = humidity;
        this.pressure = pressure;
        display();
    }

    @Override
    public void display() {
        System.out.println("Observer1: temp="+temp+",humidity="+humidity+",pressure="+pressure);
    }
}

　　观察者二实现：

public class Observer2 implements Observer,DisplayElement {
    private float temp;
    private float humidity;
    private float pressure;
    private SubSubject mySubject1;

    /*保存对Subject的引用，以后如果想取消注册，可以用到*/
    public Observer2(SubSubject mySubject1) {
        this.mySubject1 = mySubject1;
        mySubject1.addObserver(this);
    }

    @Override
    public void update(float temp, float humidity, float pressure) {
        this.temp = temp;
        this.humidity = humidity;
        this.pressure = pressure;
        display();
    }

    @Override
    public void display() {
        System.out.println("Observer2: temp="+temp+",humidity="+humidity+",pressure="+pressure);
    }
}

　　3、测试：

　　测试类：

public class ObserverTest {
    public static void main(String[] args) {
        SubSubject sub = new SubSubject();
        Observer1 observer1 = new Observer1(sub);
        Observer2 observer2 = new Observer2(sub);

        sub.setParameters(80,65,30.1f);
        sub.setParameters(70,55,20.1f);
    }
}

　　测试结果：

Observer1: temp=80.0,humidity=65.0,pressure=30.1
Observer2: temp=80.0,humidity=65.0,pressure=30.1
Observer1: temp=70.0,humidity=55.0,pressure=20.1
Observer2: temp=70.0,humidity=55.0,pressure=20.1