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The JGoodies Forms framework helps you lay out and implement elegant Swing panels quickly and consistently. It makes simple things easy and the hard stuff possible, the good design easy and the bad difficult.
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/*
 * Copyright (c) 2002-2015 JGoodies Software GmbH. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  o Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  o Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  o Neither the name of JGoodies Software GmbH nor the names of
 *    its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.jgoodies.forms.util;

import javax.swing.LookAndFeel;
import javax.swing.UIManager;

import com.jgoodies.common.base.SystemUtils;

/**
 * A library-internal class that consists only of static utility methods.
 *
 * Note: This class is not part of the public Forms API.
 * It's intended for library implementation purposes only.
 * The class's API may change at any time.
 *
 * @author Karsten Lentzsch
 * @version $Revision: 1.14 $
 *
 * @since 1.2
 */
public final class FormUtils {

    // Instance *************************************************************

    private FormUtils() {
        // Suppresses default constructor, prevents instantiation.
    }


    // API ********************************************************************

    /**
     * Lazily checks and answers whether the Aqua look&feel is active.
     *
     * @return {@code true} if the current look&feel is Aqua
     */
    public static boolean isLafAqua() {
        ensureValidCache();
        if (cachedIsLafAqua == null) {
            cachedIsLafAqua = Boolean.valueOf(SystemUtils.isLafAqua());
        }
        return cachedIsLafAqua.booleanValue();
    }


    // Caching and Lazily Computing the Laf State *****************************

    /**
     * Clears cached internal Forms state that is based
     * on the Look&Feel, for example dialog base units.
     *
     * There's typically no need to call this method directly.
     * It'll be invoked automatically, if the L&F has been changed
     * via {@link UIManager#setLookAndFeel} and cached data is requested.
     * It's been made public to allow cache invalidation for cases
     * where the L&F is changed temporarily by replacing the UIDefaults,
     * for example in a visual editor.
     *
     * @since 1.2.1
     */
    public static void clearLookAndFeelBasedCaches() {
        cachedIsLafAqua = null;
        DefaultUnitConverter.getInstance().clearCache();
    }


    /**
     * Holds the LookAndFeel that has been used to computed cached values.
     * If the current L&F differs from this cached value,
     * the caches must be cleared.
     */
    private static LookAndFeel cachedLookAndFeel;


    /**
     * Holds the cached result of the Aqua l&f check.
     * Is invalidated if a look&feel change has been detected
     * in {@code #ensureValidCache}.
     */
    private static Boolean cachedIsLafAqua;


    static void ensureValidCache() {
        LookAndFeel currentLookAndFeel = UIManager.getLookAndFeel();
        if (currentLookAndFeel != cachedLookAndFeel) {
            clearLookAndFeelBasedCaches();
            cachedLookAndFeel = currentLookAndFeel;
        }
    }


}