SE450: Observer: 5 [20/28] Previous pageContentsNext page

file:Main.java [source] [doc-public] [doc-private]
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package observer.five;
public class Main {
  public static void main(String[] argv) {
    IntObserver o = new IntObserver();
    Int c = new Int(o);
    Runnable r1 = new M(c);
    Runnable r2 = new N(c);
    for (int i=0; i<10000; i++) {
      r1.run();
      r2.run();
    }
  }
}
class IntObserver {
  private int numOps;
  public void update() {
    System.out.println (++numOps);
  }
}
class Int {
  private IntObserver o;
  public Int(IntObserver o) { this.o = o; }
  private int v;
  public int get() { return v; }
  public void inc() { v++; o.update(); }
  public void dec() { v--; o.update(); }
}
class M implements Runnable {
  private Int c;
  public M(Int c) { this.c = c; }
  public void run() {
    c.inc();
    c.inc();
    c.dec();
  }
}
class N implements Runnable {
  private Int c;
  public N(Int c) { this.c = c; }
  public void run() {
    for (int i=0; i<50; i++) {
      if (i%3==0) {
        c.dec();
      } else {
        c.inc();
      }
    }
  }
}

Observers are lazy! Subscriber is a better name.

Does Int need to know the actual class of the subscriber?

Could there be more than one subscriber?

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