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2362N/A * by Oracle in the LICENSE file that accompanied this code.
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0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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0N/A */
0N/A
0N/Apackage java.util;
0N/A
0N/A/**
0N/A * This class represents an observable object, or "data"
0N/A * in the model-view paradigm. It can be subclassed to represent an
0N/A * object that the application wants to have observed.
0N/A * <p>
0N/A * An observable object can have one or more observers. An observer
0N/A * may be any object that implements interface <tt>Observer</tt>. After an
0N/A * observable instance changes, an application calling the
0N/A * <code>Observable</code>'s <code>notifyObservers</code> method
0N/A * causes all of its observers to be notified of the change by a call
0N/A * to their <code>update</code> method.
0N/A * <p>
0N/A * The order in which notifications will be delivered is unspecified.
0N/A * The default implementation provided in the Observable class will
0N/A * notify Observers in the order in which they registered interest, but
0N/A * subclasses may change this order, use no guaranteed order, deliver
0N/A * notifications on separate threads, or may guarantee that their
0N/A * subclass follows this order, as they choose.
0N/A * <p>
0N/A * Note that this notification mechanism is has nothing to do with threads
0N/A * and is completely separate from the <tt>wait</tt> and <tt>notify</tt>
0N/A * mechanism of class <tt>Object</tt>.
0N/A * <p>
0N/A * When an observable object is newly created, its set of observers is
0N/A * empty. Two observers are considered the same if and only if the
0N/A * <tt>equals</tt> method returns true for them.
0N/A *
0N/A * @author Chris Warth
0N/A * @see java.util.Observable#notifyObservers()
0N/A * @see java.util.Observable#notifyObservers(java.lang.Object)
0N/A * @see java.util.Observer
0N/A * @see java.util.Observer#update(java.util.Observable, java.lang.Object)
0N/A * @since JDK1.0
0N/A */
0N/Apublic class Observable {
0N/A private boolean changed = false;
0N/A private Vector obs;
0N/A
0N/A /** Construct an Observable with zero Observers. */
0N/A
0N/A public Observable() {
0N/A obs = new Vector();
0N/A }
0N/A
0N/A /**
0N/A * Adds an observer to the set of observers for this object, provided
0N/A * that it is not the same as some observer already in the set.
0N/A * The order in which notifications will be delivered to multiple
0N/A * observers is not specified. See the class comment.
0N/A *
0N/A * @param o an observer to be added.
0N/A * @throws NullPointerException if the parameter o is null.
0N/A */
0N/A public synchronized void addObserver(Observer o) {
0N/A if (o == null)
0N/A throw new NullPointerException();
0N/A if (!obs.contains(o)) {
0N/A obs.addElement(o);
0N/A }
0N/A }
0N/A
0N/A /**
0N/A * Deletes an observer from the set of observers of this object.
0N/A * Passing <CODE>null</CODE> to this method will have no effect.
0N/A * @param o the observer to be deleted.
0N/A */
0N/A public synchronized void deleteObserver(Observer o) {
0N/A obs.removeElement(o);
0N/A }
0N/A
0N/A /**
0N/A * If this object has changed, as indicated by the
0N/A * <code>hasChanged</code> method, then notify all of its observers
0N/A * and then call the <code>clearChanged</code> method to
0N/A * indicate that this object has no longer changed.
0N/A * <p>
0N/A * Each observer has its <code>update</code> method called with two
0N/A * arguments: this observable object and <code>null</code>. In other
0N/A * words, this method is equivalent to:
0N/A * <blockquote><tt>
0N/A * notifyObservers(null)</tt></blockquote>
0N/A *
0N/A * @see java.util.Observable#clearChanged()
0N/A * @see java.util.Observable#hasChanged()
0N/A * @see java.util.Observer#update(java.util.Observable, java.lang.Object)
0N/A */
0N/A public void notifyObservers() {
0N/A notifyObservers(null);
0N/A }
0N/A
0N/A /**
0N/A * If this object has changed, as indicated by the
0N/A * <code>hasChanged</code> method, then notify all of its observers
0N/A * and then call the <code>clearChanged</code> method to indicate
0N/A * that this object has no longer changed.
0N/A * <p>
0N/A * Each observer has its <code>update</code> method called with two
0N/A * arguments: this observable object and the <code>arg</code> argument.
0N/A *
0N/A * @param arg any object.
0N/A * @see java.util.Observable#clearChanged()
0N/A * @see java.util.Observable#hasChanged()
0N/A * @see java.util.Observer#update(java.util.Observable, java.lang.Object)
0N/A */
0N/A public void notifyObservers(Object arg) {
0N/A /*
0N/A * a temporary array buffer, used as a snapshot of the state of
0N/A * current Observers.
0N/A */
0N/A Object[] arrLocal;
0N/A
0N/A synchronized (this) {
0N/A /* We don't want the Observer doing callbacks into
0N/A * arbitrary code while holding its own Monitor.
0N/A * The code where we extract each Observable from
0N/A * the Vector and store the state of the Observer
0N/A * needs synchronization, but notifying observers
0N/A * does not (should not). The worst result of any
0N/A * potential race-condition here is that:
0N/A * 1) a newly-added Observer will miss a
0N/A * notification in progress
0N/A * 2) a recently unregistered Observer will be
0N/A * wrongly notified when it doesn't care
0N/A */
0N/A if (!changed)
0N/A return;
0N/A arrLocal = obs.toArray();
0N/A clearChanged();
0N/A }
0N/A
0N/A for (int i = arrLocal.length-1; i>=0; i--)
0N/A ((Observer)arrLocal[i]).update(this, arg);
0N/A }
0N/A
0N/A /**
0N/A * Clears the observer list so that this object no longer has any observers.
0N/A */
0N/A public synchronized void deleteObservers() {
0N/A obs.removeAllElements();
0N/A }
0N/A
0N/A /**
0N/A * Marks this <tt>Observable</tt> object as having been changed; the
0N/A * <tt>hasChanged</tt> method will now return <tt>true</tt>.
0N/A */
0N/A protected synchronized void setChanged() {
0N/A changed = true;
0N/A }
0N/A
0N/A /**
0N/A * Indicates that this object has no longer changed, or that it has
0N/A * already notified all of its observers of its most recent change,
0N/A * so that the <tt>hasChanged</tt> method will now return <tt>false</tt>.
0N/A * This method is called automatically by the
0N/A * <code>notifyObservers</code> methods.
0N/A *
0N/A * @see java.util.Observable#notifyObservers()
0N/A * @see java.util.Observable#notifyObservers(java.lang.Object)
0N/A */
0N/A protected synchronized void clearChanged() {
0N/A changed = false;
0N/A }
0N/A
0N/A /**
0N/A * Tests if this object has changed.
0N/A *
0N/A * @return <code>true</code> if and only if the <code>setChanged</code>
0N/A * method has been called more recently than the
0N/A * <code>clearChanged</code> method on this object;
0N/A * <code>false</code> otherwise.
0N/A * @see java.util.Observable#clearChanged()
0N/A * @see java.util.Observable#setChanged()
0N/A */
0N/A public synchronized boolean hasChanged() {
0N/A return changed;
0N/A }
0N/A
0N/A /**
0N/A * Returns the number of observers of this <tt>Observable</tt> object.
0N/A *
0N/A * @return the number of observers of this object.
0N/A */
0N/A public synchronized int countObservers() {
0N/A return obs.size();
0N/A }
0N/A}