开发一个应用“观察者模式”的程序实例
时间: 2023-09-06 15:13:51 浏览: 33
好的,下面是一个简单的观察者模式的程序实例:
首先定义一个主题接口,包括添加、删除、通知观察者等方法:
```java
public interface Subject {
void registerObserver(Observer o);
void removeObserver(Observer o);
void notifyObservers();
}
```
然后定义一个观察者接口,包括接收主题通知并做出相应的方法:
```java
public interface Observer {
void update(float temperature, float humidity, float pressure);
}
```
接下来定义一个具体主题类,实现主题接口中的方法,并且在主题状态改变时通知观察者:
```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();
}
}
```
最后定义一个具体观察者类,实现观察者接口中的方法,并在主题通知时更新状态:
```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");
}
}
```
这样就可以在程序中创建主题对象和观察者对象,并将观察者注册到主题中,当主题状态改变时通知观察者更新状态。例如:
```java
public class WeatherStation {
public static void main(String[] args) {
WeatherData weatherData = new WeatherData();
CurrentConditionsDisplay currentDisplay =
new CurrentConditionsDisplay(weatherData);
weatherData.setMeasurements(80, 65, 30.4f);
weatherData.setMeasurements(82, 70, 29.2f);
weatherData.setMeasurements(78, 90, 29.2f);
}
}
```
输出结果:
```
Current conditions: 80.0F degrees and 65.0% humidity
Current conditions: 82.0F degrees and 70.0% humidity
Current conditions: 78.0F degrees and 90.0% humidity
```