1、创建观察者：
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public class SimpleObserver implements Observer{
    public SimpleObserver(SimpleObservable observable){
        observable.addObserver(this);
    }

    @Override
    public void update(Observable observable, Object data) {
        if (observable instanceof SimpleObservable) {
            SimpleObservable so = (SimpleObservable) observable;
            System.out.println("data has changed:" + so.getData());
        }

    }

}

2、创建被观察者：

public class SimpleObservable extends Observable {

    private int data = 0;
    public int getData(){
        return data;
    }
    public void setData(int data){
        if (this.data != data) {
            this.data = data;
            setChanged();
            notifyObservers();
        }
    }
}

3、测试：

public class SimpleTest extends AndroidTestCase{

    public void testObserver(){
        SimpleObservable observable = new SimpleObservable();
        SimpleObserver observer = new SimpleObserver(observable);
        observable.setData(1);
        observable.setData(1);
        observable.setData(2);
        observable.setData(3);
        observable.setData(4);
        observable.setData(4);
        observer.update(observable, null);
    }
}