124 lines
3.5 KiB
Java
124 lines
3.5 KiB
Java
// patterns/observer/ObservedFlower.java
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// (c)2021 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://OnJava8.com for more book information.
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// Demonstration of the 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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import java.util.function.*;
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@SuppressWarnings("deprecation")
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class Flower {
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private boolean isOpen = false;
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private boolean alreadyOpen = false;
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private boolean alreadyClosed = false;
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Observable opening = new Observable() {
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@Override 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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Observable closing = new Observable() {
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@Override 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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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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}
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@SuppressWarnings("deprecation")
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class Bee {
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private String id;
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Bee(String name) { id = name; }
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// Observe openings:
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public final Observer whenOpened = (ob, a) ->
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System.out.println(
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"Bee " + id + "'s breakfast time!");
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// Observe closings:
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public final Observer whenClosed = (ob, a) ->
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System.out.println(
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"Bee " + id + "'s bed time!");
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}
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@SuppressWarnings("deprecation")
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class Hummingbird {
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private String id;
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Hummingbird(String name) { id = name; }
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public final Observer whenOpened = (ob, a) ->
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System.out.println("Hummingbird " +
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id + "'s breakfast time!");
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public final Observer whenClosed = (ob, a) ->
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System.out.println("Hummingbird " +
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id + "'s bed time!");
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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.whenOpened);
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f.opening.addObserver(hb.whenOpened);
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f.opening.addObserver(ba.whenOpened);
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f.opening.addObserver(bb.whenOpened);
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f.closing.addObserver(ha.whenClosed);
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f.closing.addObserver(hb.whenClosed);
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f.closing.addObserver(ba.whenClosed);
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f.closing.addObserver(bb.whenClosed);
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// Hummingbird B decides to sleep in.
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// Removing whenOpened stops open updates.
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f.opening.deleteObserver(hb.whenOpened);
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// A change that interests observers:
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f.open();
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f.open(); // No effect: it's already open.
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System.out.println("---------------");
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// Bee A doesn't want to go to bed.
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// Removing whenClosed stops close updates.
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f.closing.deleteObserver(ba.whenClosed);
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f.close();
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System.out.println("+++++++++++++++");
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f.close(); // No effect: it's already closed.
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System.out.println("===============");
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f.opening.deleteObservers();
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f.open(); // No observers to update.
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System.out.println("###############");
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f.close(); // Close observers are still there.
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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 A's breakfast time!
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---------------
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Bee B'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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===============
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###############
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Bee B'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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