JDK8/Java8源码在线阅读

/*
 * Copyright (c) 2003, 2008, 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
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 */

package sun.java2d;

import sun.awt.image.SunVolatileImage;
import sun.awt.image.VolatileSurfaceManager;

/**
 * This factory creates platform specific VolatileSurfaceManager
 * implementations.
 *
 * There are two platform specific SurfaceManagerFactories in OpenJDK,
 * UnixSurfaceManagerFactory and WindowsSurfaceManagerFactory.
 * The actually used SurfaceManagerFactory is set by the respective platform
 * GraphicsEnvironment implementations in the static initializer.
 */
public abstract class SurfaceManagerFactory {

    /**
     * The single shared instance.
     */
    private static SurfaceManagerFactory instance;

    /**
     * Returns the surface manager factory instance. This returns a factory
     * that has been set by {@link #setInstance(SurfaceManagerFactory)}.
     *
     * @return the surface manager factory
     */
    public synchronized static SurfaceManagerFactory getInstance() {

        if (instance == null) {
            throw new IllegalStateException("No SurfaceManagerFactory set.");
        }
        return instance;
    }

    /**
     * Sets the surface manager factory. This may only be called once, and it
     * may not be set back to {@code null} when the factory is already
     * instantiated.
     *
     * @param factory the factory to set
     */
    public synchronized static void setInstance(SurfaceManagerFactory factory) {

        if (factory == null) {
            // We don't want to allow setting this to null at any time.
            throw new IllegalArgumentException("factory must be non-null");
        }

        if (instance != null) {
            // We don't want to re-set the instance at any time.
            throw new IllegalStateException("The surface manager factory is already initialized");
        }

        instance = factory;
    }

    /**
     * Creates a new instance of a VolatileSurfaceManager given any

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