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-/* Observable.java -- an object to be observed
- Copyright (C) 1999, 2000, 2001, 2002, 2005 Free Software Foundation, Inc.
-
-This file is part of GNU Classpath.
-
-GNU Classpath is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2, or (at your option)
-any later version.
-
-GNU Classpath is distributed in the hope that it will be useful, but
-WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with GNU Classpath; see the file COPYING. If not, write to the
-Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
-02110-1301 USA.
-
-Linking this library statically or dynamically with other modules is
-making a combined work based on this library. Thus, the terms and
-conditions of the GNU General Public License cover the whole
-combination.
-
-As a special exception, the copyright holders of this library give you
-permission to link this library with independent modules to produce an
-executable, regardless of the license terms of these independent
-modules, and to copy and distribute the resulting executable under
-terms of your choice, provided that you also meet, for each linked
-independent module, the terms and conditions of the license of that
-module. An independent module is a module which is not derived from
-or based on this library. If you modify this library, you may extend
-this exception to your version of the library, but you are not
-obligated to do so. If you do not wish to do so, delete this
-exception statement from your version. */
-
-
-package java.util;
-
-/**
- * This class represents an object which is observable. Other objects may
- * register their intent to be notified when this object changes; and when
- * this object does change, it will trigger the <code>update</code> method
- * of each observer.
- *
- * Note that the <code>notifyObservers()</code> method of this class is
- * unrelated to the <code>notify()</code> of Object.
- *
- * @author Warren Levy (warrenl@cygnus.com)
- * @author Eric Blake (ebb9@email.byu.edu)
- * @see Observer
- * @status updated to 1.4
- */
-public class Observable
-{
- /** Tracks whether this object has changed. */
- private boolean changed;
-
- /* List of the Observers registered as interested in this Observable. */
- private LinkedHashSet observers;
-
- /**
- * Constructs an Observable with zero Observers.
- */
- public Observable()
- {
- observers = new LinkedHashSet();
- }
-
- /**
- * Adds an Observer. If the observer was already added this method does
- * nothing.
- *
- * @param observer Observer to add
- * @throws NullPointerException if observer is null
- */
- public synchronized void addObserver(Observer observer)
- {
- if (observer == null)
- throw new NullPointerException("can't add null observer");
- observers.add(observer);
- }
-
- /**
- * Reset this Observable's state to unchanged. This is called automatically
- * by <code>notifyObservers</code> once all observers have been notified.
- *
- * @see #notifyObservers()
- */
- protected synchronized void clearChanged()
- {
- changed = false;
- }
-
- /**
- * Returns the number of observers for this object.
- *
- * @return number of Observers for this
- */
- public synchronized int countObservers()
- {
- return observers.size();
- }
-
- /**
- * Deletes an Observer of this Observable.
- *
- * @param victim Observer to delete
- */
- public synchronized void deleteObserver(Observer victim)
- {
- observers.remove(victim);
- }
-
- /**
- * Deletes all Observers of this Observable.
- */
- public synchronized void deleteObservers()
- {
- observers.clear();
- }
-
- /**
- * True if <code>setChanged</code> has been called more recently than
- * <code>clearChanged</code>.
- *
- * @return whether or not this Observable has changed
- */
- public synchronized boolean hasChanged()
- {
- return changed;
- }
-
- /**
- * If the Observable has actually changed then tell all Observers about it,
- * then reset state to unchanged.
- *
- * @see #notifyObservers(Object)
- * @see Observer#update(Observable, Object)
- */
- public void notifyObservers()
- {
- notifyObservers(null);
- }
-
- /**
- * If the Observable has actually changed then tell all Observers about it,
- * then reset state to unchanged. Note that though the order of
- * notification is unspecified in subclasses, in Observable it is in the
- * order of registration.
- *
- * @param obj argument to Observer's update method
- * @see Observer#update(Observable, Object)
- */
- public void notifyObservers(Object obj)
- {
- if (! hasChanged())
- return;
- // Create clone inside monitor, as that is relatively fast and still
- // important to keep threadsafe, but update observers outside of the
- // lock since update() can call arbitrary code.
- Set s;
- synchronized (this)
- {
- s = (Set) observers.clone();
- }
- int i = s.size();
- Iterator iter = s.iterator();
- while (--i >= 0)
- ((Observer) iter.next()).update(this, obj);
- clearChanged();
- }
-
- /**
- * Marks this Observable as having changed.
- */
- protected synchronized void setChanged()
- {
- changed = true;
- }
-}