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/* Listing1019.java */
interface Observer
{
public void update(Subject subject);
}
class Subject
{
Observer[] observers = new Observer[5];
int observerCnt = 0;
public void attach(Observer observer)
{
observers[observerCnt++] = observer;
}
public void detach(Observer observer)
{
for (int i = 0; i < observerCnt; ++i) {
if (observers[i] == observer) {
--observerCnt;
for (;i < observerCnt; ++i) {
observers[i] = observers[i + 1];
}
break;
}
}
}
public void fireUpdate()
{
for (int i = 0; i < observerCnt; ++i) {
observers[i].update(this);
}
}
}
class Counter
{
int cnt = 0;
Subject subject = new Subject();
public void attach(Observer observer)
{
subject.attach(observer);
}
public void detach(Observer observer)
{
subject.detach(observer);
}
public void inc()
{
if (++cnt % 3 == 0) {
subject.fireUpdate();
}
}
}
public class Listing1019
{
public static void main(String[] args)
{
Counter counter = new Counter();
counter.attach(
new Observer()
{
public void update(Subject subject)
{
System.out.print("divisible by 3: ");
}
}
);
while (counter.cnt < 10) {
counter.inc();
System.out.println(counter.cnt);
}
}
}
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