java设计模式

15.观察者模式：购物网站上用户添加到货通知后，商品有货后，就会主动通知订阅到货通知的用户

public interface Observer {
    public void update();
}

public class Observer1 implements Observer {
    public void update() {
        System.out.println("Observer1 has received notify");
    }
}

public class Observer2 implements Observer {
    public void update() {
        System.out.println("Observer2 has received notify");
    }
}

对用户操作接口：

public interface Subject {
    public void add(Observer observer);
    public void del(Observer observer);
    public void notifyAllObservers();
    public void operation();
}

public class AbstractObserver implements Subject {
    private Vector<Observer> vector = new Vector<Observer>();

    public void add(Observer observer) {
        vector.add(observer);
    }

    public void del(Observer observer) {
        vector.remove(observer);
    }

    public void notifyAllObservers() {
        Iterator<Observer> iterator = (Iterator<Observer>) vector.iterator();
        while (iterator.hasNext()) {
            Observer observer = iterator.next();
            observer.update();
        }
    }

    public void operation() {
        //To change body of implemented methods use File | Settings | File Templates.
    }
}

实现类：

public class MySubject extends AbstractObserver {
    public void   operation(){
        notifyAllObservers();
    }
}

public class Test {
    public static void main(String[] args) {
        Subject subject = new MySubject();
        subject.add(new Observer1());
        Observer2 observer2=new Observer2();
        subject.add(observer2);
        subject.operation();
        System.out.println("=============");
        subject.del(observer2);
        subject.operation();

    }
}

如果要增加其他通知类型，可以在Observer接口新增方法，例如消息推送，

16.迭代器模式：先顺序访问对象，再对对象中元素遍历访问，例如Iterator ite=Collection.iterator         ite.hasNext();

public interface Iterator {
    public Object previous();
    public Object next();
    public boolean hasNext();
    public Object first();
}

public interface Collection {
    public Iterator iterator();
    public Object get(int i);
    public int size();
}

Collection中可以获取Iterator

public class MyCollection implements Collection {
    String[] strings = {"a","b","c"};
    public Iterator iterator() {
        return new MyIterator(this);  //To change body of implemented methods use File | Settings | File Templates.
    }

    public Object get(int i) {
        return strings[i];  //To change body of implemented methods use File | Settings | File Templates.
    }

    public int size() {
        return strings.length;  //To change body of implemented methods use File | Settings | File Templates.
    }
}

 

public class MyIterator implements Iterator {
    private int pos = -1;
    private Collection collection;

    public MyIterator(Collection collection) {
        this.collection = collection;
    }

    public Object previous() {
        if (pos > 0) {
            pos--;
        }
        return collection.get(pos);  //To change body of implemented methods use File | Settings | File Templates.
    }

    public Object next() {
        if (pos < collection.size() - 1) {
            pos++;
        }
        return collection.get(pos);  //To change body of implemented methods use File | Settings | File Templates.
    }

    public boolean hasNext() {
        if (pos < collection.size() - 1) {
            return true;
        }
        return false;
    }

    public Object first() {
        if (collection.size() > 0) {
            return collection.get(0);
        }
        return null;
    }
}

测试类：

public class Test {
    public static void main(String[] args) {
        Collection collection = new MyCollection();
        Iterator iterator = collection.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }

    }
}

           

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