src/java.desktop/share/classes/sun/awt/SunDisplayChanger.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
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package sun.awt;

import java.awt.IllegalComponentStateException;
import java.util.Collections;
import java.util.Iterator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;

import sun.util.logging.PlatformLogger;

/**
 * This class is used to aid in keeping track of DisplayChangedListeners and
 * notifying them when a display change has taken place. DisplayChangedListeners
 * are notified when the display's bit depth is changed, or when a top-level
 * window has been dragged onto another screen.
 *
 * It is safe for a DisplayChangedListener to be added while the list is being
 * iterated.
 *
 * The displayChanged() call is propagated after some occurrence (either
 * due to user action or some other application) causes the display mode
 * (e.g., depth or resolution) to change.  All heavyweight components need
 * to know when this happens because they need to create new surfaceData
 * objects based on the new depth.
 *
 * displayChanged() is also called on Windows when they are moved from one
 * screen to another on a system equipped with multiple displays.
 */
public class SunDisplayChanger {

    private static final PlatformLogger log = PlatformLogger.getLogger("sun.awt.multiscreen.SunDisplayChanger");

    // Create a new synchronized map with initial capacity of one listener.
    // It is asserted that the most common case is to have one GraphicsDevice
    // and one top-level Window.
    private Map<DisplayChangedListener, Void> listeners =
        Collections.synchronizedMap(new WeakHashMap<DisplayChangedListener, Void>(1));

    public SunDisplayChanger() {}

    /*
     * Add a DisplayChangeListener to this SunDisplayChanger so that it is
     * notified when the display is changed.
     */
    public void add(DisplayChangedListener theListener) {
        if (log.isLoggable(PlatformLogger.Level.FINE)) {
            if (theListener == null) {
                log.fine("Assertion (theListener != null) failed");
            }
        }
        if (log.isLoggable(PlatformLogger.Level.FINER)) {
            log.finer("Adding listener: " + theListener);
        }
        listeners.put(theListener, null);
    }

    /*
     * Remove the given DisplayChangeListener from this SunDisplayChanger.
     */
    public void remove(DisplayChangedListener theListener) {
        if (log.isLoggable(PlatformLogger.Level.FINE)) {
            if (theListener == null) {
                log.fine("Assertion (theListener != null) failed");
            }
        }
        if (log.isLoggable(PlatformLogger.Level.FINER)) {
            log.finer("Removing listener: " + theListener);
        }
        listeners.remove(theListener);
    }

    /*
     * Notify our list of DisplayChangedListeners that a display change has
     * taken place by calling their displayChanged() methods.
     */
    public void notifyListeners() {
        if (log.isLoggable(PlatformLogger.Level.FINEST)) {
            log.finest("notifyListeners");
        }
    // This method is implemented by making a clone of the set of listeners,
    // and then iterating over the clone.  This is because during the course
    // of responding to a display change, it may be appropriate for a
    // DisplayChangedListener to add or remove itself from a SunDisplayChanger.
    // If the set itself were iterated over, rather than a clone, it is
    // trivial to get a ConcurrentModificationException by having a
    // DisplayChangedListener remove itself from its list.
    // Because all display change handling is done on the event thread,
    // synchronization provides no protection against modifying the listener
    // list while in the middle of iterating over it.  -bchristi 7/10/2001

        Set<DisplayChangedListener> cloneSet;

        synchronized(listeners) {
            cloneSet = new HashSet<DisplayChangedListener>(listeners.keySet());
        }

        for (DisplayChangedListener current : cloneSet) {
            try {
                if (log.isLoggable(PlatformLogger.Level.FINEST)) {
                    log.finest("displayChanged for listener: " + current);
                }
                current.displayChanged();
            } catch (IllegalComponentStateException e) {
                // This DisplayChangeListener is no longer valid.  Most
                // likely, a top-level window was dispose()d, but its
                // Java objects have not yet been garbage collected.  In any
                // case, we no longer need to track this listener, though we
                // do need to remove it from the original list, not the clone.
                listeners.remove(current);
            }
        }
    }

    /*
     * Notify our list of DisplayChangedListeners that a palette change has
     * taken place by calling their paletteChanged() methods.
     */
    public void notifyPaletteChanged() {
        if (log.isLoggable(PlatformLogger.Level.FINEST)) {
            log.finest("notifyPaletteChanged");
        }
    // This method is implemented by making a clone of the set of listeners,
    // and then iterating over the clone.  This is because during the course
    // of responding to a display change, it may be appropriate for a
    // DisplayChangedListener to add or remove itself from a SunDisplayChanger.
    // If the set itself were iterated over, rather than a clone, it is
    // trivial to get a ConcurrentModificationException by having a
    // DisplayChangedListener remove itself from its list.
    // Because all display change handling is done on the event thread,
    // synchronization provides no protection against modifying the listener
    // list while in the middle of iterating over it.  -bchristi 7/10/2001

        Set<DisplayChangedListener> cloneSet;

        synchronized (listeners) {
            cloneSet = new HashSet<DisplayChangedListener>(listeners.keySet());
        }
        for (DisplayChangedListener current : cloneSet) {
            try {
                if (log.isLoggable(PlatformLogger.Level.FINEST)) {
                    log.finest("paletteChanged for listener: " + current);
                }
                current.paletteChanged();
            } catch (IllegalComponentStateException e) {
                // This DisplayChangeListener is no longer valid.  Most
                // likely, a top-level window was dispose()d, but its
                // Java objects have not yet been garbage collected.  In any
                // case, we no longer need to track this listener, though we
                // do need to remove it from the original list, not the clone.
                listeners.remove(current);
            }
        }
    }
}