Softwaredesign: Beispiel: Beobachter
| Softwaredesign: Beispiel: Beobachter |
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import java.util.Vector;
abstract
public
class Subject {
private
Vector observers;
//--------------------
protected
Subject() {
observers = new Vector();
}
//--------------------
public
synchronized
void addObserver(Observer o) {
observers.addElement(o);
o.setSubject(this); // link back
}
//--------------------
public
synchronized
void removeObserver(Observer o) {
observers.removeElement(o);
o.setSubject(null); // remove link back
}
//--------------------
public
synchronized
void notifyObservers() {
Vector o = (Vector)(observers.clone());
for ( int i = 0, max = o.size();
i < max;
++i ) {
((Observer)(o.elementAt(i))).update();
}
}
}
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abstract
public
class Observer {
protected
Subject s;
public
void setSubject(Subject s) {
this.s = s;
}
abstract
public
void update();
}
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public
class Clock extends Subject {
private
int seconds;
//--------------------
public
int getTime() {
return
seconds;
}
//--------------------
public
int getMinutes() {
return
seconds / 60;
}
//--------------------
public
void setTime(int seconds) {
this.seconds = seconds;
notifyObservers(); // state changed
}
//--------------------
public
void tick() {
++seconds;
notifyObservers(); // state changed
}
}
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public
class ClockObserver1 extends Observer {
public
void update() {
Clock c = (Clock)s; // downcast !!!
System.out.println("time in seconds is " + c.getTime());
}
}
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public
class ClockObserver2 extends Observer {
private
int minutes = -1; // observer state
//--------------------
public
void update() {
Clock c = (Clock)s; // downcast !!!
int minutes = c.getMinutes();
// output only if observer state changes
if ( minutes != this.minutes ) {
this.minutes = minutes;
System.out.println("time in minutes is " + minutes);
}
}
}
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| Letzte Änderung: 13.04.2012 | © Prof. Dr. Uwe Schmidt |
