OnJava8-Examples/patterns/observer/ObservedFlower.java

//: patterns/observer/ObservedFlower.java
// ©2015 MindView LLC: see Copyright.txt
// Demonstration of "observer" pattern.
package patterns.observer;
import java.util.*;
import static com.mindviewinc.util.Print.*;

class Flower {
  private boolean isOpen;
  private OpenNotifier oNotify =
    new OpenNotifier();
  private CloseNotifier cNotify =
    new CloseNotifier();
  public Flower() { isOpen = false; }
  public void open() { // Opens its petals
    isOpen = true;
    oNotify.notifyObservers();
    cNotify.open();
  }
  public void close() { // Closes its petals
    isOpen = false;
    cNotify.notifyObservers();
    oNotify.close();
  }
  public Observable opening() {
    return oNotify;
  }
  public Observable closing() {
    return cNotify;
  }
  private class OpenNotifier extends Observable {
    private boolean alreadyOpen = false;
    @Override
    public void notifyObservers() {
      if(isOpen && !alreadyOpen) {
        setChanged();
        super.notifyObservers();
        alreadyOpen = true;
      }
    }
    public void close() { alreadyOpen = false; }
  }
  private class CloseNotifier extends Observable{
    private boolean alreadyClosed = false;
    @Override
    public void notifyObservers() {
      if(!isOpen && !alreadyClosed) {
        setChanged();
        super.notifyObservers();
        alreadyClosed = true;
      }
    }
    public void open() { alreadyClosed = false; }
  }
}

class Bee {
  private String name;
  private OpenObserver openObsrv =
    new OpenObserver();
  private CloseObserver closeObsrv =
    new CloseObserver();
  public Bee(String nm)  { name = nm; }
  // An inner class for observing openings:
  private class OpenObserver implements Observer{
    @Override
    public void update(Observable ob, Object a) {
      print("Bee " + name + "'s breakfast time!");
    }
  }
  // Another inner class for closings:
  private class CloseObserver implements Observer{
    @Override
    public void update(Observable ob, Object a) {
      print("Bee " + name + "'s bed time!");
    }
  }
  public Observer openObserver() {
    return openObsrv;
  }
  public Observer closeObserver() {
    return closeObsrv;
  }
}

class Hummingbird {
  private String name;
  private OpenObserver openObsrv =
    new OpenObserver();
  private CloseObserver closeObsrv =
    new CloseObserver();
  public Hummingbird(String nm) { name = nm; }
  private class OpenObserver implements Observer{
    @Override
    public void update(Observable ob, Object a) {
      print("Hummingbird " + name +
        "'s breakfast time!");
    }
  }
  private class CloseObserver implements Observer{
    @Override
    public void update(Observable ob, Object a) {
      print("Hummingbird " + name + "'s bed time!");
    }
  }
  public Observer openObserver() {
    return openObsrv;
  }
  public Observer closeObserver() {
    return closeObsrv;
  }
}

public class ObservedFlower {
  public static void main(String args[]) {
    Flower f = new Flower();
    Bee
      ba = new Bee("A"),
      bb = new Bee("B");
    Hummingbird
      ha = new Hummingbird("A"),
      hb = new Hummingbird("B");
    f.opening().addObserver(ha.openObserver());
    f.opening().addObserver(hb.openObserver());
    f.opening().addObserver(ba.openObserver());
    f.opening().addObserver(bb.openObserver());
    f.closing().addObserver(ha.closeObserver());
    f.closing().addObserver(hb.closeObserver());
    f.closing().addObserver(ba.closeObserver());
    f.closing().addObserver(bb.closeObserver());
    // Hummingbird B decides to sleep in:
    f.opening().deleteObserver(hb.openObserver());
    // A change that interests observers:
    f.open();
    f.open(); // It's already open, no change.
    // Bee A doesn't want to go to bed:
    f.closing().deleteObserver(ba.closeObserver());
    f.close();
    f.close(); // It's already closed; no change
    f.opening().deleteObservers();
    f.open();
    f.close();
  }
} /* Output:
Bee B's breakfast time!
Bee A's breakfast time!
Hummingbird A's breakfast time!
Bee B's bed time!
Hummingbird B's bed time!
Hummingbird A's bed time!
Bee B's bed time!
Hummingbird B's bed time!
Hummingbird A's bed time!
*///:~