JDK8/Java8源码在线阅读

/*
 * Copyright (c) 2003, 2005, 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 javax.swing.plaf.metal;

import java.awt.*;
import javax.swing.*;
import javax.swing.plaf.ComponentUI;
import javax.swing.plaf.UIResource;
import javax.swing.plaf.basic.*;

/**
 * Metal implementation of <code>MenuBarUI</code>. This class is responsible
 * for providing the metal look and feel for <code>JMenuBar</code>s.
 *
 * @see javax.swing.plaf.MenuBarUI
 * @since 1.5
 */
public class MetalMenuBarUI extends BasicMenuBarUI  {
    /**
     * Creates the <code>ComponentUI</code> implementation for the passed
     * in component.
     *
     * @param x JComponent to create the ComponentUI implementation for
     * @return ComponentUI implementation for <code>x</code>
     * @throws NullPointerException if <code>x</code> is null
     */
    public static ComponentUI createUI(JComponent x) {
        if (x == null) {
            throw new NullPointerException("Must pass in a non-null component");
        }
        return new MetalMenuBarUI();
    }

    /**
     * Configures the specified component appropriate for the metal look and
     * feel.
     *
     * @param c the component where this UI delegate is being installed
     * @throws NullPointerException if <code>c</code> is null.
     */
    public void installUI(JComponent c) {
        super.installUI(c);
        MetalToolBarUI.register(c);
    }

    /**
     * Reverses configuration which was done on the specified component during
     * <code>installUI</code>.
     *
     * @param c the component where this UI delegate is being installed
     * @throws NullPointerException if <code>c</code> is null.
     */
    public void uninstallUI(JComponent c) {
        super.uninstallUI(c);
        MetalToolBarUI.unregister(c);
    }

    /**
     * If necessary paints the background of the component, then
     * invokes <code>paint</code>.
     *
     * @param g Graphics to paint to
     * @param c JComponent painting on
     * @throws NullPointerException if <code>g</code> or <code>c</code> is
     *         null
     * @see javax.swing.plaf.ComponentUI#update
     * @see javax.swing.plaf.ComponentUI#paint
     * @since 1.5
     */
    public void update(Graphics g, JComponent c) {
        boolean isOpaque = c.isOpaque();
        if (g == null) {
            throw new NullPointerException("Graphics must be non-null");
        }
        if (isOpaque && (c.getBackground() instanceof UIResource) &&
                        UIManager.get("MenuBar.gradient") != null) {
            if (MetalToolBarUI.doesMenuBarBorderToolBar((JMenuBar)c)) {
                JToolBar tb = (JToolBar)MetalToolBarUI.
                     findRegisteredComponentOfType(c, JToolBar.class);
                if (tb.isOpaque() &&tb.getBackground() instanceof UIResource) {
                    MetalUtils.drawGradient(c, g, "MenuBar.gradient", 0, 0,

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