JDK8/Java8源码在线阅读

/*
 * Copyright (c) 2005, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package sun.awt;

import java.awt.Component;
import java.awt.Rectangle;
import java.awt.event.PaintEvent;

/**
 * PaintEventDispatcher is responsible for dispatching PaintEvents.  There
 * can be only one PaintEventDispatcher active at a particular time.
 *
 */
public class PaintEventDispatcher {
    /**
     * Singleton dispatcher.
     */
    private static PaintEventDispatcher dispatcher;

    /**
     * Sets the current <code>PaintEventDispatcher</code>.
     *
     * @param dispatcher PaintEventDispatcher
     */
    public static void setPaintEventDispatcher(
                          PaintEventDispatcher dispatcher) {
        synchronized(PaintEventDispatcher.class) {
            PaintEventDispatcher.dispatcher = dispatcher;
        }
    }

    /**
     * Returns the currently active <code>PaintEventDispatcher</code>.  This
     * will never return null.
     *
     * @return PaintEventDispatcher
     */
    public static PaintEventDispatcher getPaintEventDispatcher() {
        synchronized(PaintEventDispatcher.class) {
            if (dispatcher == null) {
                dispatcher = new PaintEventDispatcher();
            }
            return dispatcher;
        }
    }

    /**
     * Creates and returns the <code>PaintEvent</code> that should be
     * dispatched for the specified component.  If this returns null
     * no <code>PaintEvent</code> is dispatched.
     * <p>
     * <b>WARNING:</b> This is invoked from the native thread, be careful
     * what methods you end up invoking here.
     */
    public PaintEvent createPaintEvent(Component target, int x, int y, int w,
                                       int h) {

        return new PaintEvent(target, PaintEvent.PAINT,
                              new Rectangle(x, y, w, h));
    }

    /**
     * Returns true if a native background erase should be done for
     * the specified Component.
     */
    public boolean shouldDoNativeBackgroundErase(Component c) {
        return true;
    }

    /**
     * This method is invoked from the toolkit thread when the surface

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