写个观察者模式demo
时间: 2023-09-02 18:07:18 浏览: 49
观察者模式是一种设计模式,它定义了一种一对多的依赖关系,让多个观察者对象同时监听某一个主题对象,当主题对象发生变化时,它的所有依赖者(观察者)都会自动收到通知并更新。
以下是一个简单的观察者模式的demo:
首先,我们定义一个主题接口,它包括添加、删除和通知观察者的方法:
```java
public interface Subject {
void registerObserver(Observer o);
void removeObserver(Observer o);
void notifyObservers();
}
```
然后,我们定义一个观察者接口:
```java
public interface Observer {
void update(float temperature, float humidity, float pressure);
}
```
接下来,我们实现一个具体的主题类,它包含状态(温度、湿度、气压)和一组观察者:
```java
public class WeatherData implements Subject {
private ArrayList<Observer> observers;
private float temperature;
private float humidity;
private float pressure;
public WeatherData() {
observers = new ArrayList<Observer>();
}
public void registerObserver(Observer o) {
observers.add(o);
}
public void removeObserver(Observer o) {
int i = observers.indexOf(o);
if (i >= 0) {
observers.remove(i);
}
}
public void notifyObservers() {
for (int i = 0; i < observers.size(); i++) {
Observer observer = (Observer)observers.get(i);
observer.update(temperature, humidity, pressure);
}
}
public void measurementsChanged() {
notifyObservers();
}
public void setMeasurements(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
measurementsChanged();
}
}
```
最后,我们实现一个具体的观察者类:
```java
public class CurrentConditionsDisplay implements Observer {
private float temperature;
private float humidity;
private Subject weatherData;
public CurrentConditionsDisplay(Subject weatherData) {
this.weatherData = weatherData;
weatherData.registerObserver(this);
}
public void update(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
display();
}
public void display() {
System.out.println("Current conditions: " + temperature + "F degrees and " + humidity + "% humidity");
}
}
```
现在,我们可以创建一个WeatherData对象,并添加一个CurrentConditionsDisplay观察者:
```java
WeatherData weatherData = new WeatherData();
CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);
```
然后,我们可以模拟气象站测量温度、湿度和气压,并更新WeatherData对象:
```java
weatherData.setMeasurements(80, 65, 30.4f);
```
此时,CurrentConditionsDisplay观察者会自动收到通知并更新显示。