Head First设计模式笔记（观察者模式--jdk自带实现）

1.主题类

package com.TWO;import java.util.Observable;public class WeatherData extends Observable {    private float temp;    private float humidity;    private float pressure;    public WeatherData(){}    public void measurementsChanged(){        //在调用notifyObservers()之前，要先调用setChanged来指示状态已经改变        setChanged();        notifyObservers();    }    public void setMeasurements(float temp,float humidity,float pressure){        this.temp = temp;        this.humidity = humidity;        this.pressure = pressure;        measurementsChanged();    }    public float getTemperature(){        return temp;    }    public float getHumidity(){        return humidity;    }    public float getPressure(){        return pressure;    }}

2.观察者

package com.TWO;import java.util.Observable;import java.util.Observer;public class CurrentConditionsDisplay implements Observer{    Observable observable;    private float temp;    private float humidity;    public CurrentConditionsDisplay(Observable observable) {        this.observable = observable;        observable.addObserver(this);    }    @Override    public void update(Observable o, Object arg) {        if(o instanceof WeatherData){            WeatherData weatherData = (WeatherData)o;            this.temp = weatherData.getTemperature();            this.humidity = weatherData.getHumidity();            display();        }    }    public void display(){        System.out.println("temp = "+ temp +";humidity = "+ humidity);    }}

测试类

package com.TWO;public class Main {    public static void main(String[] args){        WeatherData weatherData = new WeatherData();        new CurrentConditionsDisplay(weatherData);        //模拟数据变化        weatherData.setMeasurements(30, 40, 50);    }}