JDK是如何支持观察者模式的？举例说明其实现方式。

import java.util.Observable;
import java.util.Observer;

// 具体的观察者类，实现Observer接口
class CurrentConditionsDisplay implements Observer {
    private float temperature;
    private float humidity;

    @Override
    public void update(Observable o, Object arg) {
        if (o instanceof WeatherData) {
            WeatherData weatherData = (WeatherData) o;
            this.temperature = weatherData.getTemperature();
            this.humidity = weatherData.getHumidity();
            display();
        }
    }

    public void display() {
        System.out.println("Current conditions: " + temperature + "F degrees and " + humidity + "% humidity");
    }
}

// 具体的被观察者类，实现Observable类
class WeatherData extends Observable {
    private float temperature;
    private float humidity;

    // 设置天气数据
    public void setMeasurements(float temperature, float humidity) {
        this.temperature = temperature;
        this.humidity = humidity;
        setChanged(); // 标记数据发生了变化
        notifyObservers(); // 通知所有观察者
    }

    public float getTemperature() {
        return temperature;
    }

    public float getHumidity() {
        return humidity;
    }
}

// 测试
public class WeatherStation {
    public static void main(String[] args) {
        WeatherData weatherData = new WeatherData();
        CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay();

        // 注册观察者
        weatherData.addObserver(currentDisplay);

        // 设置天气数据，触发通知
        weatherData.setMeasurements(80, 65);
        weatherData.setMeasurements(82, 70);
    }
}