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HeadFirst设计模式之观察者模式

摘要：
1、 什么是观察者模式观察者模式定义了对象之间的一系列一对多关系。当主题对象的状态发生变化时，将通知所有观察者。2.定制观察模式1.2.1packageheadfirst.designpatterns.observer.weather；23publicinterfaceSubject｛4publicvoidregisterObserver（Observer）；5publicvoidremoveObs

一、什么是观察者模式

观察者模式定义了一系列对象间一对多的关系，当主题对象的状态发生变化时，会通知所有观察者

二、自定义观察模式

1.HeadFirst设计模式之观察者模式第1张HeadFirst设计模式之观察者模式第2张HeadFirst设计模式之观察者模式第3张HeadFirst设计模式之观察者模式第4张

2.

1 package headfirst.designpatterns.observer.weather;
2 
3 public interface Subject {
4     public void registerObserver(Observer o);
5     public void removeObserver(Observer o);
6     public void notifyObservers();
7 }

3.

1 package headfirst.designpatterns.observer.weather;
2 
3 public interface Observer {
4     public void update(float temp, float humidity, float pressure);
5 }

4.

 1 package headfirst.designpatterns.observer.weather;
 2 
 3 import java.util.*;
 4 
 5 public class WeatherData implements Subject {
 6     private ArrayList<Observer> observers;
 7     private float temperature;
 8     private float humidity;
 9     private float pressure;
10     
11     public WeatherData() {
12         observers = new ArrayList<Observer>();
13     }
14     
15     public void registerObserver(Observer o) {
16         observers.add(o);
17     }
18     
19     public void removeObserver(Observer o) {
20         int i = observers.indexOf(o);
21         if (i >= 0) {
22             observers.remove(i);
23         }
24     }
25     
26     public void notifyObservers() {
27         for (Observer observer : observers) {
28             observer.update(temperature, humidity, pressure);
29         }
30     }
31     
32     public void measurementsChanged() {
33         notifyObservers();
34     }
35     
36     public void setMeasurements(float temperature, float humidity, float pressure) {
37         this.temperature = temperature;
38         this.humidity = humidity;
39         this.pressure = pressure;
40         measurementsChanged();
41     }
42 
43     public float getTemperature() {
44         return temperature;
45     }
46     
47     public float getHumidity() {
48         return humidity;
49     }
50     
51     public float getPressure() {
52         return pressure;
53     }
54 
55 }

5.

 1 package headfirst.designpatterns.observer.weather;
 2 
 3 public class StatisticsDisplay implements Observer, DisplayElement {
 4     private float maxTemp = 0.0f;
 5     private float minTemp = 200;
 6     private float tempSum= 0.0f;
 7     private int numReadings;
 8     private WeatherData weatherData;
 9 
10     public StatisticsDisplay(WeatherData weatherData) {
11         this.weatherData = weatherData;
12         weatherData.registerObserver(this);
13     }
14 
15     public void update(float temp, float humidity, float pressure) {
16         tempSum += temp;
17         numReadings++;
18 
19         if (temp > maxTemp) {
20             maxTemp = temp;
21         }
22  
23         if (temp < minTemp) {
24             minTemp = temp;
25         }
26 
27         display();
28     }
29 
30     public void display() {
31         System.out.println("Avg/Max/Min temperature = " + (tempSum / numReadings)
32             + "/" + maxTemp + "/" + minTemp);
33     }
34 }

6.

package headfirst.designpatterns.observer.weather;

public interface DisplayElement {
    public void display();
}

7.

 1 package headfirst.designpatterns.observer.weather;
 2     
 3 public class CurrentConditionsDisplay implements Observer, DisplayElement {
 4     private float temperature;
 5     private float humidity;
 6     private Subject weatherData;
 7     
 8     public CurrentConditionsDisplay(Subject weatherData) {
 9         this.weatherData = weatherData;
10         weatherData.registerObserver(this);
11     }
12     
13     public void update(float temperature, float humidity, float pressure) {
14         this.temperature = temperature;
15         this.humidity = humidity;
16         display();
17     }
18     
19     public void display() {
20         System.out.println("Current conditions: " + temperature 
21             + "F degrees and " + humidity + "% humidity");
22     }
23 }

8.

 1 package headfirst.designpatterns.observer.weather;
 2 
 3 public class HeatIndexDisplay implements Observer, DisplayElement {
 4     float heatIndex = 0.0f;
 5     private WeatherData weatherData;
 6 
 7     public HeatIndexDisplay(WeatherData weatherData) {
 8         this.weatherData = weatherData;
 9         weatherData.registerObserver(this);
10     }
11 
12     public void update(float t, float rh, float pressure) {
13         heatIndex = computeHeatIndex(t, rh);
14         display();
15     }
16     
17     private float computeHeatIndex(float t, float rh) {
18         float index = (float)((16.923 + (0.185212 * t) + (5.37941 * rh) - (0.100254 * t * rh) 
19             + (0.00941695 * (t * t)) + (0.00728898 * (rh * rh)) 
20             + (0.000345372 * (t * t * rh)) - (0.000814971 * (t * rh * rh)) +
21             (0.0000102102 * (t * t * rh * rh)) - (0.000038646 * (t * t * t)) + (0.0000291583 * 
22             (rh * rh * rh)) + (0.00000142721 * (t * t * t * rh)) + 
23             (0.000000197483 * (t * rh * rh * rh)) - (0.0000000218429 * (t * t * t * rh * rh)) +
24             0.000000000843296 * (t * t * rh * rh * rh)) -
25             (0.0000000000481975 * (t * t * t * rh * rh * rh)));
26         return index;
27     }
28 
29     public void display() {
30         System.out.println("Heat index is " + heatIndex);
31     }
32 }

9.

 1 package headfirst.designpatterns.observer.weather;
 2 
 3 public class WeatherStation {
 4 
 5     public static void main(String[] args) {
 6         WeatherData weatherData = new WeatherData();
 7     
 8         CurrentConditionsDisplay currentDisplay = 
 9             new CurrentConditionsDisplay(weatherData);
10         StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
11         ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);
12 
13         weatherData.setMeasurements(80, 65, 30.4f);
14         weatherData.setMeasurements(82, 70, 29.2f);
15         weatherData.setMeasurements(78, 90, 29.2f);
16     }
17 }

10.

 1 package headfirst.designpatterns.observer.weather;
 2 
 3 public class WeatherStationHeatIndex {
 4 
 5     public static void main(String[] args) {
 6         WeatherData weatherData = new WeatherData();
 7         CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);
 8         StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
 9         ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);
10         HeatIndexDisplay heatIndexDisplay = new HeatIndexDisplay(weatherData);
11 
12         weatherData.setMeasurements(80, 65, 30.4f);
13         weatherData.setMeasurements(82, 70, 29.2f);
14         weatherData.setMeasurements(78, 90, 29.2f);
15     }
16 }

三、Java.util.Observable

1.

1 package headfirst.designpatterns.observer.weatherobservable;
2 
3 public interface DisplayElement {
4     public void display();
5 }

2.

 1 package headfirst.designpatterns.observer.weatherobservable;
 2     
 3 import java.util.Observable;
 4     
 5 public class WeatherData extends Observable {
 6     private float temperature;
 7     private float humidity;
 8     private float pressure;
 9     
10     public WeatherData() { }
11     
12     public void measurementsChanged() {
13         setChanged();
14         notifyObservers();
15     }
16     
17     public void setMeasurements(float temperature, float humidity, float pressure) {
18         this.temperature = temperature;
19         this.humidity = humidity;
20         this.pressure = pressure;
21         measurementsChanged();
22     }
23     
24     public float getTemperature() {
25         return temperature;
26     }
27     
28     public float getHumidity() {
29         return humidity;
30     }
31     
32     public float getPressure() {
33         return pressure;
34     }
35 }

3.

 1 package headfirst.designpatterns.observer.weatherobservable;
 2 
 3 import java.util.Observable;
 4 import java.util.Observer;
 5 
 6 public class StatisticsDisplay implements Observer, DisplayElement {
 7     private float maxTemp = 0.0f;
 8     private float minTemp = 200;
 9     private float tempSum= 0.0f;
10     private int numReadings;
11 
12     public StatisticsDisplay(Observable observable) {
13         observable.addObserver(this);
14     }
15 
16     public void update(Observable observable, Object arg) {
17         if (observable instanceof WeatherData) {
18             WeatherData weatherData = (WeatherData)observable;
19             float temp = weatherData.getTemperature();
20             tempSum += temp;
21             numReadings++;
22 
23             if (temp > maxTemp) {
24                 maxTemp = temp;
25             }
26  
27             if (temp < minTemp) {
28                 minTemp = temp;
29             }
30 
31             display();
32         }
33     }
34 
35     public void display() {
36         System.out.println("Avg/Max/Min temperature = " + (tempSum / numReadings)
37             + "/" + maxTemp + "/" + minTemp);
38     }
39 }

4.

 1 package headfirst.designpatterns.observer.weatherobservable;
 2 
 3 import java.util.Observable;
 4 import java.util.Observer;
 5 
 6 public class HeatIndexDisplay implements Observer, DisplayElement {
 7     float heatIndex = 0.0f;
 8 
 9     public HeatIndexDisplay(Observable observable) {
10         observable.addObserver(this);
11     }
12 
13     public void update(Observable observable, Object arg) {
14         if (observable instanceof WeatherData) {
15             WeatherData weatherData = (WeatherData)observable;
16             float t = weatherData.getTemperature();
17             float rh = weatherData.getHumidity();
18             heatIndex = (float)
19                 (
20                 (16.923 + (0.185212 * t)) + 
21                 (5.37941 * rh) - 
22                 (0.100254 * t * rh) + 
23                 (0.00941695 * (t * t)) + 
24                 (0.00728898 * (rh * rh)) + 
25                 (0.000345372 * (t * t * rh)) - 
26                 (0.000814971 * (t * rh * rh)) +
27                 (0.0000102102 * (t * t * rh * rh)) - 
28                 (0.000038646 * (t * t * t)) + 
29                 (0.0000291583 * (rh * rh * rh)) +
30                 (0.00000142721 * (t * t * t * rh)) + 
31                 (0.000000197483 * (t * rh * rh * rh)) - 
32                 (0.0000000218429 * (t * t * t * rh * rh)) +
33                 (0.000000000843296 * (t * t * rh * rh * rh)) -
34                 (0.0000000000481975 * (t * t * t * rh * rh * rh)));
35             display();
36         }
37     }
38 
39     public void display() {
40         System.out.println("Heat index is " + heatIndex);
41     }
42 }

5.

 1 package headfirst.designpatterns.observer.weatherobservable;
 2 
 3 import java.util.Observable;
 4 import java.util.Observer;
 5 
 6 public class ForecastDisplay implements Observer, DisplayElement {
 7     private float currentPressure = 29.92f;  
 8     private float lastPressure;
 9 
10     public ForecastDisplay(Observable observable) {
11         observable.addObserver(this);
12     }
13 
14     public void update(Observable observable, Object arg) {
15         if (observable instanceof WeatherData) {
16             WeatherData weatherData = (WeatherData)observable;
17             lastPressure = currentPressure;
18             currentPressure = weatherData.getPressure();
19             display();
20         }
21     }
22 
23     public void display() {
24         System.out.print("Forecast: ");
25         if (currentPressure > lastPressure) {
26             System.out.println("Improving weather on the way!");
27         } else if (currentPressure == lastPressure) {
28             System.out.println("More of the same");
29         } else if (currentPressure < lastPressure) {
30             System.out.println("Watch out for cooler, rainy weather");
31         }
32     }
33 }

6.

 1 package headfirst.designpatterns.observer.weatherobservable;
 2 
 3 public class WeatherStation {
 4 
 5     public static void main(String[] args) {
 6         WeatherData weatherData = new WeatherData();
 7         
 8         CurrentConditionsDisplay currentConditions = new CurrentConditionsDisplay(weatherData);
 9         StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
10         ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);
11 
12         weatherData.setMeasurements(80, 65, 30.4f);
13         weatherData.setMeasurements(82, 70, 29.2f);
14         weatherData.setMeasurements(78, 90, 29.2f);
15     }
16 }

四、Swing中的观察者模式

1.

 1 package headfirst.observer.swing;
 2     
 3 import java.awt.*;
 4 import java.awt.event.*;
 5 import javax.swing.*;
 6 import javax.swing.event.*;
 7     
 8 public class SwingObserverExample {
 9     JFrame frame;
10     
11     public static void main(String[] args) {
12         SwingObserverExample example = new SwingObserverExample();
13         example.go();
14     }
15     
16     public void go() {
17         frame = new JFrame();
18 
19         JButton button = new JButton("Should I do it?");
20         button.addActionListener(new AngelListener());
21         button.addActionListener(new DevilListener());
22         frame.getContentPane().add(BorderLayout.CENTER, button);
23 
24         // Set frame properties 
25         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
26         frame.getContentPane().add(BorderLayout.CENTER, button);
27         frame.setSize(300,300);
28         frame.setVisible(true);
29     }
30     
31     class AngelListener implements ActionListener {
32         public void actionPerformed(ActionEvent event) {
33             System.out.println("Don't do it, you might regret it!");
34         }
35     }
36 
37     class DevilListener implements ActionListener {
38         public void actionPerformed(ActionEvent event) {
39             System.out.println("Come on, do it!");
40         }
41     }
42 }

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