javax/swing/LookAndFeel.java

/*
 * Copyright (c) 1997, 2017, 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;

import java.awt.Font;
import java.awt.event.InputEvent;
import java.awt.event.KeyEvent;
import java.awt.Color;
import java.awt.Component;
import java.awt.SystemColor;
import java.awt.Toolkit;
import sun.awt.SunToolkit;

import javax.swing.text.*;
import javax.swing.border.*;
import javax.swing.plaf.*;

import java.net.URL;
import sun.swing.SwingUtilities2;
import sun.swing.DefaultLayoutStyle;
import sun.swing.ImageIconUIResource;

import java.util.StringTokenizer;


/**
 * {@code LookAndFeel}, as the name implies, encapsulates a look and
 * feel. Beyond installing a look and feel most developers never need to
 * interact directly with {@code LookAndFeel}. In general only developers
 * creating a custom look and feel need to concern themselves with this class.
 * <p>
 * Swing is built upon the foundation that each {@code JComponent}
 * subclass has an implementation of a specific {@code ComponentUI}
 * subclass. The {@code ComponentUI} is often referred to as "the ui",
 * "component ui", or "look and feel delegate". The {@code ComponentUI}
 * subclass is responsible for providing the look and feel specific
 * functionality of the component. For example, {@code JTree} requires
 * an implementation of the {@code ComponentUI} subclass {@code
 * TreeUI}. The implementation of the specific {@code
 * ComponentUI} subclass is provided by the {@code LookAndFeel}. Each
 * {@code JComponent} subclass identifies the {@code ComponentUI}
 * subclass it requires by way of the {@code JComponent} method {@code
 * getUIClassID}.
 * <p>
 * Each {@code LookAndFeel} implementation must provide
 * an implementation of the appropriate {@code ComponentUI} subclass by
 * specifying a value for each of Swing's ui class ids in the {@code
 * UIDefaults} object returned from {@code getDefaults}. For example,
 * {@code BasicLookAndFeel} uses {@code BasicTreeUI} as the concrete
 * implementation for {@code TreeUI}. This is accomplished by {@code
 * BasicLookAndFeel} providing the key-value pair {@code
 * "TreeUI"-"javax.swing.plaf.basic.BasicTreeUI"}, in the
 * {@code UIDefaults} returned from {@code getDefaults}. Refer to
 * {@link UIDefaults#getUI(JComponent)} for details on how the implementation
 * of the {@code ComponentUI} subclass is obtained.
 * <p>
 * When a {@code LookAndFeel} is installed the {@code UIManager} does
 * not check that an entry exists for all ui class ids. As such,
 * random exceptions will occur if the current look and feel has not
 * provided a value for a particular ui class id and an instance of
 * the {@code JComponent} subclass is created.
 *
 * <h2>Recommendations for Look and Feels</h2>
 *
 * As noted in {@code UIManager} each {@code LookAndFeel} has the opportunity
 * to provide a set of defaults that are layered in with developer and
 * system defaults. Some of Swing's components require the look and feel
 * to provide a specific set of defaults. These are documented in the
 * classes that require the specific default.
 *
 * <h3><a id="defaultRecommendation">ComponentUIs and defaults</a></h3>
 *
 * All {@code ComponentUIs} typically need to set various properties
 * on the {@code JComponent} the {@code ComponentUI} is providing the
 * look and feel for. This is typically done when the {@code
 * ComponentUI} is installed on the {@code JComponent}. Setting a
 * property should only be done if the developer has not set the
 * property. For non-primitive values it is recommended that the
 * {@code ComponentUI} only change the property on the {@code
 * JComponent} if the current value is {@code null} or implements
 * {@code UIResource}. If the current value is {@code null} or
 * implements {@code UIResource} it indicates the property has not
 * been set by the developer, and the ui is free to change it.  For
 * example, {@code BasicButtonUI.installDefaults} only changes the
 * font on the {@code JButton} if the return value from {@code
 * button.getFont()} is {@code null} or implements {@code
 * UIResource}. On the other hand if {@code button.getFont()} returned
 * a {@code non-null} value that did not implement {@code UIResource}
 * then {@code BasicButtonUI.installDefaults} would not change the
 * {@code JButton}'s font.
 * <p>
 * For primitive values, such as {@code opaque}, the method {@code
 * installProperty} should be invoked.  {@code installProperty} only changes
 * the corresponding property if the value has not been changed by the
 * developer.
 * <p>
 * {@code ComponentUI} implementations should use the various install methods
 * provided by this class as they handle the necessary checking and install
 * the property using the recommended guidelines.
 *
 * <h3><a id="exceptions"></a>Exceptions</h3>
 *
 * All of the install methods provided by {@code LookAndFeel} need to
 * access the defaults if the value of the property being changed is
 * {@code null} or a {@code UIResource}. For example, installing the
 * font does the following:
 * <pre>
 *   JComponent c;
 *   Font font = c.getFont();
 *   if (font == null || (font instanceof UIResource)) {
 *       c.setFont(UIManager.getFont("fontKey"));
 *   }
 * </pre>
 * If the font is {@code null} or a {@code UIResource}, the
 * defaults table is queried with the key {@code fontKey}. All of
 * {@code UIDefault's} get methods throw a {@code
 * NullPointerException} if passed in {@code null}. As such, unless
 * otherwise noted each of the various install methods of {@code
 * LookAndFeel} throw a {@code NullPointerException} if the current
 * value is {@code null} or a {@code UIResource} and the supplied
 * defaults key is {@code null}. In addition, unless otherwise specified
 * all of the {@code install} methods throw a {@code NullPointerException} if
 * a {@code null} component is passed in.
 *
 * @author Tom Ball
 * @author Hans Muller
 * @since 1.2
 */
public abstract class LookAndFeel
{

    /**
     * Convenience method for setting a component's foreground
     * and background color properties with values from the
     * defaults.  The properties are only set if the current
     * value is either {@code null} or a {@code UIResource}.
     *
     * @param c component to set the colors on
     * @param defaultBgName key for the background
     * @param defaultFgName key for the foreground
     *
     * @see #installColorsAndFont
     * @see UIManager#getColor
     * @throws NullPointerException as described in
     *         <a href="#exceptions">exceptions</a>
     */
    public static void installColors(JComponent c,
                                     String defaultBgName,
                                     String defaultFgName)
    {
        Color bg = c.getBackground();
        if (bg == null || bg instanceof UIResource) {
            c.setBackground(UIManager.getColor(defaultBgName));
        }

        Color fg = c.getForeground();
        if (fg == null || fg instanceof UIResource) {
            c.setForeground(UIManager.getColor(defaultFgName));
        }
    }


    /**
     * Convenience method for setting a component's foreground,
     * background and font properties with values from the
     * defaults.  The properties are only set if the current
     * value is either {@code null} or a {@code UIResource}.
     *
     * @param c component set to the colors and font on
     * @param defaultBgName key for the background
     * @param defaultFgName key for the foreground
     * @param defaultFontName key for the font
     * @throws NullPointerException as described in
     *         <a href="#exceptions">exceptions</a>
     *
     * @see #installColors
     * @see UIManager#getColor
     * @see UIManager#getFont
     */
    public static void installColorsAndFont(JComponent c,
                                         String defaultBgName,
                                         String defaultFgName,
                                         String defaultFontName) {
        Font f = c.getFont();
        if (f == null || f instanceof UIResource) {
            c.setFont(UIManager.getFont(defaultFontName));
        }

        installColors(c, defaultBgName, defaultFgName);
    }


    /**
     * Convenience method for setting a component's border property with
     * a value from the defaults. The border is only set if the border is
     * {@code null} or an instance of {@code UIResource}.
     *
     * @param c component to set the border on
     * @param defaultBorderName key specifying the border
     * @throws NullPointerException as described in
     *         <a href="#exceptions">exceptions</a>
     */
    public static void installBorder(JComponent c, String defaultBorderName) {
        Border b = c.getBorder();
        if (b == null || b instanceof UIResource) {
            c.setBorder(UIManager.getBorder(defaultBorderName));
        }
    }


    /**
     * Convenience method for uninstalling a border. If the border of
     * the component is a {@code UIResource}, it is set to {@code
     * null}.
     *
     * @param c component to uninstall the border on
     * @throws NullPointerException if {@code c} is {@code null}
     */
    public static void uninstallBorder(JComponent c) {
        if (c.getBorder() instanceof UIResource) {
            c.setBorder(null);
        }
    }

    /**
     * Convenience method for installing a property with the specified name
     * and value on a component if that property has not already been set
     * by the developer.  This method is intended to be used by
     * ui delegate instances that need to specify a default value for a
     * property of primitive type (boolean, int, ..), but do not wish
     * to override a value set by the client.  Since primitive property
     * values cannot be wrapped with the {@code UIResource} marker, this method
     * uses private state to determine whether the property has been set
     * by the client.
     *
     * @throws IllegalArgumentException if the specified property is not
     *         one which can be set using this method
     * @throws ClassCastException if the property value has not been set
     *         by the developer and the type does not match the property's type
     * @throws NullPointerException if {@code c} is {@code null}, or the
     *         named property has not been set by the developer and
     *         {@code propertyValue} is {@code null}
     * @param c target component to set the property on
     * @param propertyName name of the property to set
     * @param propertyValue value of the property
     * @since 1.5
     */
    public static void installProperty(JComponent c,
                                       String propertyName, Object propertyValue) {
        // this is a special case because the JPasswordField's ancestor hierarchy
        // includes a class outside of javax.swing, thus we cannot call setUIProperty
        // directly.
        if (SunToolkit.isInstanceOf(c, "javax.swing.JPasswordField")) {
            if (!((JPasswordField)c).customSetUIProperty(propertyName, propertyValue)) {
                c.setUIProperty(propertyName, propertyValue);
            }
        } else {
            c.setUIProperty(propertyName, propertyValue);
        }
    }

    /**
     * Convenience method for building an array of {@code
     * KeyBindings}. While this method is not deprecated, developers
     * should instead use {@code ActionMap} and {@code InputMap} for
     * supplying key bindings.
     * <p>
     * This method returns an array of {@code KeyBindings}, one for each
     * alternating {@code key-action} pair in {@code keyBindingList}.
     * A {@code key} can either be a {@code String} in the format
     * specified by the <code>KeyStroke.getKeyStroke</code> method, or
     * a {@code KeyStroke}. The {@code action} part of the pair is a
     * {@code String} that corresponds to the name of the {@code
     * Action}.
     * <p>
     * The following example illustrates creating a {@code KeyBinding} array
     * from six alternating {@code key-action} pairs:
     * <pre>
     *  JTextComponent.KeyBinding[] multilineBindings = makeKeyBindings( new Object[] {
     *          "UP", DefaultEditorKit.upAction,
     *        "DOWN", DefaultEditorKit.downAction,
     *     "PAGE_UP", DefaultEditorKit.pageUpAction,
     *   "PAGE_DOWN", DefaultEditorKit.pageDownAction,
     *       "ENTER", DefaultEditorKit.insertBreakAction,
     *         "TAB", DefaultEditorKit.insertTabAction
     *  });
     * </pre>
     * If {@code keyBindingList's} length is odd, the last element is
     * ignored.
     * <p>
     * Supplying a {@code null} value for either the {@code key} or
     * {@code action} part of the {@code key-action} pair results in
     * creating a {@code KeyBinding} with the corresponding value
     * {@code null}. As other parts of Swing's expect {@code non-null} values
     * in a {@code KeyBinding}, you should avoid supplying {@code null} as
     * either the {@code key} or {@code action} part of the {@code key-action}
     * pair.
     *
     * @param keyBindingList an array of {@code key-action} pairs
     * @return an array of {@code KeyBindings}
     * @throws NullPointerException if {@code keyBindingList} is {@code null}
     * @throws ClassCastException if the {@code key} part of the pair is
     *         not a {@code KeyStroke} or {@code String}, or the
     *         {@code action} part of the pair is not a {@code String}
     * @see ActionMap
     * @see InputMap
     * @see KeyStroke#getKeyStroke
     */
    public static JTextComponent.KeyBinding[] makeKeyBindings(Object[] keyBindingList)
    {
        JTextComponent.KeyBinding[] rv = new JTextComponent.KeyBinding[keyBindingList.length / 2];

        for(int i = 0; i < rv.length; i ++) {
            Object o = keyBindingList[2 * i];
            KeyStroke keystroke = (o instanceof KeyStroke)
                ? (KeyStroke) o
                : KeyStroke.getKeyStroke((String) o);
            String action = (String) keyBindingList[2 * i + 1];
            rv[i] = new JTextComponent.KeyBinding(keystroke, action);
        }

        return rv;
    }

    /**
     * Creates an {@code InputMapUIResource} from <code>keys</code>. This is
     * a convenience method for creating a new {@code InputMapUIResource},
     * invoking {@code loadKeyBindings(map, keys)}, and returning the
     * {@code InputMapUIResource}.
     *
     * @param keys alternating pairs of {@code keystroke-action key}
     *        pairs as described in {@link #loadKeyBindings}
     * @return newly created and populated {@code InputMapUIResource}
     * @see #loadKeyBindings
     *
     * @since 1.3
     */
    public static InputMap makeInputMap(Object[] keys) {
        InputMap retMap = new InputMapUIResource();
        loadKeyBindings(retMap, keys);
        return retMap;
    }

    /**
     * Creates a {@code ComponentInputMapUIResource} from
     * <code>keys</code>. This is a convenience method for creating a
     * new {@code ComponentInputMapUIResource}, invoking {@code
     * loadKeyBindings(map, keys)}, and returning the {@code
     * ComponentInputMapUIResource}.
     *
     * @param c component to create the {@code ComponentInputMapUIResource}
     *          with
     * @param keys alternating pairs of {@code keystroke-action key}
     *        pairs as described in {@link #loadKeyBindings}
     * @return newly created and populated {@code InputMapUIResource}
     * @throws IllegalArgumentException if {@code c} is {@code null}
     *
     * @see #loadKeyBindings
     * @see ComponentInputMapUIResource
     *
     * @since 1.3
     */
    public static ComponentInputMap makeComponentInputMap(JComponent c,
                                                          Object[] keys) {
        ComponentInputMap retMap = new ComponentInputMapUIResource(c);
        loadKeyBindings(retMap, keys);
        return retMap;
    }


    /**
     * Populates an {@code InputMap} with the specified bindings.
     * The bindings are supplied as a list of alternating
     * {@code keystroke-action key} pairs. The {@code keystroke} is either
     * an instance of {@code KeyStroke}, or a {@code String}
     * that identifies the {@code KeyStroke} for the binding. Refer
     * to {@code KeyStroke.getKeyStroke(String)} for the specific
     * format. The {@code action key} part of the pair is the key
     * registered in the {@code InputMap} for the {@code KeyStroke}.
     * <p>
     * The following illustrates loading an {@code InputMap} with two
     * {@code key-action} pairs:
     * <pre>
     *   LookAndFeel.loadKeyBindings(inputMap, new Object[] {
     *     "control X", "cut",
     *     "control V", "paste"
     *   });
     * </pre>
     * <p>
     * Supplying a {@code null} list of bindings ({@code keys}) does not
     * change {@code retMap} in any way.
     * <p>
     * Specifying a {@code null} {@code action key} results in
     * removing the {@code keystroke's} entry from the {@code InputMap}.
     * A {@code null} {@code keystroke} is ignored.
     *
     * @param retMap {@code InputMap} to add the {@code key-action}
     *               pairs to
     * @param keys bindings to add to {@code retMap}
     * @throws NullPointerException if {@code keys} is
     *         {@code non-null}, not empty, and {@code retMap} is
     *         {@code null}
     *
     * @see KeyStroke#getKeyStroke(String)
     * @see InputMap
     *
     * @since 1.3
     */
    public static void loadKeyBindings(InputMap retMap, Object[] keys) {
        if (keys != null) {
            for (int counter = 0, maxCounter = keys.length;
                 counter < maxCounter; counter++) {
                Object keyStrokeO = keys[counter++];
                KeyStroke ks = (keyStrokeO instanceof KeyStroke) ?
                                (KeyStroke)keyStrokeO :
                                KeyStroke.getKeyStroke((String)keyStrokeO);
                retMap.put(ks, keys[counter]);
            }
        }
    }

    /**
     * Creates and returns a {@code UIDefault.LazyValue} that loads an
     * image. The returned value is an implementation of {@code
     * UIDefaults.LazyValue}. When {@code createValue} is invoked on
     * the returned object, the image is loaded. If the image is {@code
     * non-null}, it is then wrapped in an {@code Icon} that implements {@code
     * UIResource}. The image is loaded using {@code
     * Class.getResourceAsStream(gifFile)}.
     * <p>
     * This method does not check the arguments in any way. It is
     * strongly recommended that {@code non-null} values are supplied else
     * exceptions may occur when {@code createValue} is invoked on the
     * returned object.
     *
     * @param baseClass {@code Class} used to load the resource
     * @param gifFile path to the image to load
     * @return a {@code UIDefaults.LazyValue}; when resolved the
     *         {@code LazyValue} loads the specified image
     * @see UIDefaults.LazyValue
     * @see Icon
     * @see Class#getResourceAsStream(String)
     */
    public static Object makeIcon(final Class<?> baseClass, final String gifFile) {
        return SwingUtilities2.makeIcon_Unprivileged(baseClass, baseClass, gifFile);
    }

    /**
     * Returns the <code>LayoutStyle</code> for this look
     * and feel.  This never returns {@code null}.
     * <p>
     * You generally don't use the <code>LayoutStyle</code> from
     * the look and feel, instead use the <code>LayoutStyle</code>
     * method <code>getInstance</code>.
     *
     * @see LayoutStyle#getInstance
     * @return the <code>LayoutStyle</code> for this look and feel
     * @since 1.6
     */
    public LayoutStyle getLayoutStyle() {
        return DefaultLayoutStyle.getInstance();
    }

    /**
     * Invoked when the user attempts an invalid operation,
     * such as pasting into an uneditable <code>JTextField</code>
     * that has focus. The default implementation beeps. Subclasses
     * that wish different behavior should override this and provide
     * the additional feedback.
     *
     * @param component the <code>Component</code> the error occurred in,
     *                  may be <code>null</code>
     *                  indicating the error condition is not directly
     *                  associated with a <code>Component</code>
     * @since 1.4
     */
    public void provideErrorFeedback(Component component) {
        Toolkit toolkit = null;
        if (component != null) {
            toolkit = component.getToolkit();
        } else {
            toolkit = Toolkit.getDefaultToolkit();
        }
        toolkit.beep();
    } // provideErrorFeedback()

    /**
     * Returns the value of the specified system desktop property by
     * invoking <code>Toolkit.getDefaultToolkit().getDesktopProperty()</code>.
     * If the value of the specified property is {@code null},
     * {@code fallbackValue} is returned.
     *
     * @param systemPropertyName the name of the system desktop property being queried
     * @param fallbackValue the object to be returned as the value if the system value is null
     * @return the current value of the desktop property
     *
     * @see java.awt.Toolkit#getDesktopProperty
     *
     * @since 1.4
     */
    public static Object getDesktopPropertyValue(String systemPropertyName, Object fallbackValue) {
        Object value = Toolkit.getDefaultToolkit().getDesktopProperty(systemPropertyName);
        if (value == null) {
            return fallbackValue;
        } else if (value instanceof Color) {
            return new ColorUIResource((Color)value);
        } else if (value instanceof Font) {
            return new FontUIResource((Font)value);
        }
        return value;
    }

    /**
     * Returns an <code>Icon</code> with a disabled appearance.
     * This method is used to generate a disabled <code>Icon</code> when
     * one has not been specified.  For example, if you create a
     * <code>JButton</code> and only specify an <code>Icon</code> via
     * <code>setIcon</code> this method will be called to generate the
     * disabled <code>Icon</code>. If {@code null} is passed as
     * <code>icon</code> this method returns {@code null}.
     * <p>
     * Some look and feels might not render the disabled {@code Icon}, in which
     * case they will ignore this.
     *
     * @param component {@code JComponent} that will display the {@code Icon},
     *         may be {@code null}
     * @param icon {@code Icon} to generate the disabled icon from
     * @return disabled {@code Icon}, or {@code null} if a suitable
     *         {@code Icon} can not be generated
     * @since 1.5
     */
    public Icon getDisabledIcon(JComponent component, Icon icon) {
        if (icon instanceof ImageIcon) {
            return new ImageIconUIResource(GrayFilter.
                   createDisabledImage(((ImageIcon)icon).getImage()));
        }
        return null;
    }

    /**
     * Returns an <code>Icon</code> for use by disabled
     * components that are also selected. This method is used to generate an
     * <code>Icon</code> for components that are in both the disabled and
     * selected states but do not have a specific <code>Icon</code> for this
     * state.  For example, if you create a <code>JButton</code> and only
     * specify an <code>Icon</code> via <code>setIcon</code> this method
     * will be called to generate the disabled and selected
     * <code>Icon</code>. If {@code null} is passed as <code>icon</code> this
     * methods returns {@code null}.
     * <p>
     * Some look and feels might not render the disabled and selected
     * {@code Icon}, in which case they will ignore this.
     *
     * @param component {@code JComponent} that will display the {@code Icon},
     *        may be {@code null}
     * @param icon {@code Icon} to generate disabled and selected icon from
     * @return disabled and selected icon, or {@code null} if a suitable
     *         {@code Icon} can not be generated.
     * @since 1.5
     */
    public Icon getDisabledSelectedIcon(JComponent component, Icon icon) {
        return getDisabledIcon(component, icon);
    }

    /**
     * Return a short string that identifies this look and feel, e.g.
     * "CDE/Motif".  This string should be appropriate for a menu item.
     * Distinct look and feels should have different names, e.g.
     * a subclass of MotifLookAndFeel that changes the way a few components
     * are rendered should be called "CDE/Motif My Way"; something
     * that would be useful to a user trying to select a L&amp;F from a list
     * of names.
     *
     * @return short identifier for the look and feel
     */
    public abstract String getName();


    /**
     * Return a string that identifies this look and feel.  This string
     * will be used by applications/services that want to recognize
     * well known look and feel implementations.  Presently
     * the well known names are "Motif", "Windows", "Mac", "Metal".  Note
     * that a LookAndFeel derived from a well known superclass
     * that doesn't make any fundamental changes to the look or feel
     * shouldn't override this method.
     *
     * @return identifier for the look and feel
     */
    public abstract String getID();


    /**
     * Return a one line description of this look and feel implementation,
     * e.g. "The CDE/Motif Look and Feel".   This string is intended for
     * the user, e.g. in the title of a window or in a ToolTip message.
     *
     * @return short description for the look and feel
     */
    public abstract String getDescription();


    /**
     * Returns {@code true} if the <code>LookAndFeel</code> returned
     * <code>RootPaneUI</code> instances support providing {@code Window}
     * decorations in a <code>JRootPane</code>.
     * <p>
     * The default implementation returns {@code false}, subclasses that
     * support {@code Window} decorations should override this and return
     * {@code true}.
     *
     * @return {@code true} if the {@code RootPaneUI} instances created by
     *         this look and feel support client side decorations
     * @see JDialog#setDefaultLookAndFeelDecorated
     * @see JFrame#setDefaultLookAndFeelDecorated
     * @see JRootPane#setWindowDecorationStyle
     * @since 1.4
     */
    public boolean getSupportsWindowDecorations() {
        return false;
    }

    /**
     * If the underlying platform has a "native" look and feel, and
     * this is an implementation of it, return {@code true}.  For
     * example, when the underlying platform is Solaris running CDE
     * a CDE/Motif look and feel implementation would return {@code
     * true}.
     *
     * @return {@code true} if this look and feel represents the underlying
     *         platform look and feel
     */
    public abstract boolean isNativeLookAndFeel();


    /**
     * Return {@code true} if the underlying platform supports and or permits
     * this look and feel.  This method returns {@code false} if the look
     * and feel depends on special resources or legal agreements that
     * aren't defined for the current platform.
     *
     *
     * @return {@code true} if this is a supported look and feel
     * @see UIManager#setLookAndFeel
     */
    public abstract boolean isSupportedLookAndFeel();


    /**
     * Initializes the look and feel. While this method is public,
     * it should only be invoked by the {@code UIManager} when a
     * look and feel is installed as the current look and feel. This
     * method is invoked before the {@code UIManager} invokes
     * {@code getDefaults}. This method is intended to perform any
     * initialization for the look and feel. Subclasses
     * should do any one-time setup they need here, rather than
     * in a static initializer, because look and feel class objects
     * may be loaded just to discover that {@code isSupportedLookAndFeel()}
     * returns {@code false}.
     *
     * @see #uninitialize
     * @see UIManager#setLookAndFeel
     */
    public void initialize() {
    }


    /**
     * Uninitializes the look and feel. While this method is public,
     * it should only be invoked by the {@code UIManager} when
     * the look and feel is uninstalled. For example,
     * {@code UIManager.setLookAndFeel} invokes this when the look and
     * feel is changed.
     * <p>
     * Subclasses may choose to free up some resources here.
     *
     * @see #initialize
     * @see UIManager#setLookAndFeel
     */
    public void uninitialize() {
    }

    /**
     * Returns the look and feel defaults. While this method is public,
     * it should only be invoked by the {@code UIManager} when the
     * look and feel is set as the current look and feel and after
     * {@code initialize} has been invoked.
     *
     * @return the look and feel defaults
     * @see #initialize
     * @see #uninitialize
     * @see UIManager#setLookAndFeel
     */
    public UIDefaults getDefaults() {
        return null;
    }

    /**
     * Returns a string that displays and identifies this
     * object's properties.
     *
     * @return a String representation of this object
     */
    public String toString() {
        return "[" + getDescription() + " - " + getClass().getName() + "]";
    }
}