123 lines
3.3 KiB
Java
123 lines
3.3 KiB
Java
// patterns/observer/ObservedFlower.java
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// (c)2016 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
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// Demonstration of "Observer" pattern
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// {java patterns.observer.ObservedFlower}
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package patterns.observer;
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import java.util.*;
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class Flower {
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private boolean isOpen;
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private boolean alreadyOpen;
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private boolean alreadyClosed;
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public Flower() { isOpen = false; }
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OpenNotifier opening = new OpenNotifier();
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CloseNotifier closing = new CloseNotifier();
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public void open() { // Opens its petals
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isOpen = true;
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opening.notifyObservers();
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alreadyClosed = false;
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}
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public void close() { // Closes its petals
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isOpen = false;
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closing.notifyObservers();
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alreadyOpen = false;
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}
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class OpenNotifier extends Observable {
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@Override
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public void notifyObservers() {
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if(isOpen && !alreadyOpen) {
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setChanged();
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super.notifyObservers();
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alreadyOpen = true;
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}
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}
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}
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class CloseNotifier extends Observable{
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@Override
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public void notifyObservers() {
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if(!isOpen && !alreadyClosed) {
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setChanged();
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super.notifyObservers();
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alreadyClosed = true;
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}
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}
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}
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}
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class Bee {
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private String name;
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public Bee(String nm) { name = nm; }
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// Observe openings:
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public Observer openObserver() {
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return (ob, a) -> System.out.println(
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"Bee " + name + "'s breakfast time!");
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}
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// Observe closings:
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public Observer closeObserver() {
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return (ob, a) -> System.out.println(
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"Bee " + name + "'s bed time!");
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}
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}
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class Hummingbird {
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private String name;
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public Hummingbird(String nm) { name = nm; }
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public Observer openObserver() {
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return (ob, a) -> System.out.println(
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"Hummingbird " + name +
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"'s breakfast time!");
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}
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public Observer closeObserver() {
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return (ob, a) -> System.out.println(
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"Hummingbird " + name + "'s bed time!");
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}
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}
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public class ObservedFlower {
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public static void main(String[] args) {
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Flower f = new Flower();
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Bee
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ba = new Bee("A"),
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bb = new Bee("B");
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Hummingbird
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ha = new Hummingbird("A"),
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hb = new Hummingbird("B");
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f.opening.addObserver(ha.openObserver());
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f.opening.addObserver(hb.openObserver());
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f.opening.addObserver(ba.openObserver());
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f.opening.addObserver(bb.openObserver());
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f.closing.addObserver(ha.closeObserver());
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f.closing.addObserver(hb.closeObserver());
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f.closing.addObserver(ba.closeObserver());
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f.closing.addObserver(bb.closeObserver());
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// Hummingbird B decides to sleep in:
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f.opening.deleteObserver(hb.openObserver());
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// A change that interests observers:
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f.open();
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f.open(); // It's already open, no change.
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// Bee A doesn't want to go to bed:
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f.closing.deleteObserver(ba.closeObserver());
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f.close();
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f.close(); // It's already closed; no change
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f.opening.deleteObservers();
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f.open();
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f.close();
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}
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}
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/* Output:
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Bee B's breakfast time!
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Bee A's breakfast time!
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Hummingbird B's breakfast time!
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Hummingbird A's breakfast time!
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Bee B's bed time!
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Bee A's bed time!
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Hummingbird B's bed time!
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Hummingbird A's bed time!
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Bee B's bed time!
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Bee A's bed time!
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Hummingbird B's bed time!
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Hummingbird A's bed time!
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*/
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