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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/java/util/Observable.java
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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;
+ }
+}