Java观察者模式

  • 小时候我们都看过动画片<<葫芦啦>>,孩子们,不要管我!快打妖精!(这是爷爷的经典台词)看着动画化片,做着英雄梦。问题来了,电视中的画面用代码如何实现呢?
  • 与其临渊羡鱼,不如退而结网。让我们一步一步来实现

huluwa


1. 首先定义爷爷
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
import java.util.Observable;
/**
* Created by zhangfeng on 2016/10/17.
* 爷爷,消息发布者
*/
public class Grandpa extends Observable {
private String mName;
public Grandpa(String name) {
mName = name;
}
/**
* 向葫芦娃发出求救消息
* @param msg
*/
public void sendMsg(String msg) {
setChanged();
notifyObservers(msg);
}
public String getName() {
return mName;
}
public void setName(String name) {
mName = name;
}
}
爷爷是消息发布者,当有情况时会调用 sendMsg()方法给你葫芦娃发消息,它继承 java的Observable
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
public class Observable {
List<Observer> observers = new ArrayList<Observer>();
boolean changed = false;
public Observable() {
}
public void addObserver(Observer observer) {
if (observer == null) {
throw new NullPointerException("observer == null");
}
synchronized (this) {
if (!observers.contains(observer))
observers.add(observer);
}
}
protected void clearChanged() {
changed = false;
}
public int countObservers() {
return observers.size();
}
public synchronized void deleteObserver(Observer observer) {
observers.remove(observer);
}
public synchronized void deleteObservers() {
observers.clear();
}
public boolean hasChanged() {
return changed;
}
public void notifyObservers() {
notifyObservers(null);
}
@SuppressWarnings("unchecked")
public void notifyObservers(Object data) {
int size = 0;
Observer[] arrays = null;
synchronized (this) {
if (hasChanged()) {
clearChanged();
size = observers.size();
arrays = new Observer[size];
observers.toArray(arrays);
}
}
if (arrays != null) {
for (Observer observer : arrays) {
observer.update(this, data);
}
}
}
protected void setChanged() {
changed = true;
}
}
Observable 里保存着一个 Observer 的集合,然后提供了添加、删除、提醒等方法。其中重要的是 notifyObservers(…) 方法,当确定出事了(changed 为 true)时 ,挨个通知葫芦娃
Observer 是一个接口,规定了葫芦娃收到消息的方法 update(…)
1
2
3
public interface Observer {
void update(Observable observable, Object data);
}
2. 定义葫芦娃 LagenariaSicerariaChildren,葫芦娃需要按规矩来,实现 Observer 接口:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
import android.util.Log;
import java.util.Observable;
import java.util.Observer;
/**
* Created by zhangfeng on 2016/10/17.
* 葫芦娃,消息接收者
*/
public class LagenariaSicerariaChildren implements Observer {
String mName;
public LagenariaSicerariaChildren(String name){
mName = name;
}
/**
* 接收到爷爷的求救消息
* @param observable
* @param data
*/
@Override
public void update(Observable observable, Object data) {
Grandpa writer;
if (observable instanceof Grandpa) {
writer = (Grandpa) observable;
Log.i("----",getName() + "收到" + writer.getName() + " 的求救: " + data.toString());
}
}
public String getName() {
return mName;
}
public void setName(String name) {
mName = name;
}
}
3. 葫芦娃去爷爷那登记
1
2
3
4
5
6
7
8
9
10
11
//爷爷出厂
Grandpa grandpa = new Grandpa("爷爷");
//种下一颗葫芦籽
LagenariaSicerariaChildren penhuo = new LagenariaSicerariaChildren("喷火娃");
//再种一颗葫芦籽
LagenariaSicerariaChildren penshui = new LagenariaSicerariaChildren("喷水娃");
//葫芦娃认亲(爷爷)
grandpa.addObserver(penhuo);
grandpa.addObserver(penshui);
//爷爷有危险向葫芦娃发出求救
grandpa.sendMsg("孩儿们,蛇精来了,快来救我!");
4. 最后结果
1
2
喷水娃收到爷爷 的求救: 孩儿们,蛇精来了,快来救我!
喷火娃收到爷爷 的求救: 孩儿们,蛇精来了,快来救我!