src/java.desktop/share/classes/javax/swing/DefaultListCellRenderer.java

/*
 * Copyright (c) 1998, 2024, 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.Color;
import java.awt.Component;
import java.awt.Rectangle;
import java.io.Serializable;

import javax.swing.border.Border;
import javax.swing.border.EmptyBorder;
import javax.swing.plaf.synth.SynthListUI;

import sun.swing.DefaultLookup;
import sun.swing.SwingUtilities2;

/**
 * Renders an item in a list.
 * <p>
 * <strong><a id="override">Implementation Note:</a></strong>
 * This class overrides
 * <code>invalidate</code>,
 * <code>validate</code>,
 * <code>revalidate</code>,
 * <code>repaint</code>,
 * <code>isOpaque</code>,
 * and
 * <code>firePropertyChange</code>
 * solely to improve performance.
 * If not overridden, these frequently called methods would execute code paths
 * that are unnecessary for the default list cell renderer.
 * If you write your own renderer,
 * take care to weigh the benefits and
 * drawbacks of overriding these methods.
 *
 * <p>
 *
 * <strong>Warning:</strong>
 * Serialized objects of this class will not be compatible with
 * future Swing releases. The current serialization support is
 * appropriate for short term storage or RMI between applications running
 * the same version of Swing.  As of 1.4, support for long term storage
 * of all JavaBeans
 * has been added to the <code>java.beans</code> package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @author Philip Milne
 * @author Hans Muller
 * @since 1.2
 */
@SuppressWarnings("serial") // Same-version serialization only
public class DefaultListCellRenderer extends JLabel
    implements ListCellRenderer<Object>, Serializable
{

   /**
    * An empty <code>Border</code>. This field might not be used. To change the
    * <code>Border</code> used by this renderer override the
    * <code>getListCellRendererComponent</code> method and set the border
    * of the returned component directly.
    */
    private static final Border DEFAULT_NO_FOCUS_BORDER = new EmptyBorder(1, 1, 1, 1);
    /**
     * No focus border
     */
    protected static Border noFocusBorder = DEFAULT_NO_FOCUS_BORDER;

    /**
     * Constructs a default renderer object for an item
     * in a list.
     */
    public DefaultListCellRenderer() {
        super();
        setOpaque(true);
        setBorder(getNoFocusBorder());
        setName("List.cellRenderer");
    }

    private Border getNoFocusBorder() {
        Border border = DefaultLookup.getBorder(this, ui, "List.cellNoFocusBorder");
        if (border != null &&
                (noFocusBorder == null ||
                noFocusBorder == DEFAULT_NO_FOCUS_BORDER)) {
            return border;
        }
        return noFocusBorder;
    }

    public Component getListCellRendererComponent(
        JList<?> list,
        Object value,
        int index,
        boolean isSelected,
        boolean cellHasFocus)
    {
        setComponentOrientation(list.getComponentOrientation());

        Color bg = null;
        Color fg = null;

        JList.DropLocation dropLocation = list.getDropLocation();
        if (dropLocation != null
                && !dropLocation.isInsert()
                && dropLocation.getIndex() == index) {

            bg = DefaultLookup.getColor(this, ui, "List.dropCellBackground");
            fg = DefaultLookup.getColor(this, ui, "List.dropCellForeground");

            isSelected = true;
        }

        if (isSelected) {
            setBackground(bg == null ? list.getSelectionBackground() : bg);
            setForeground(fg == null ? list.getSelectionForeground() : fg);
        }
        else {
            setBackground(list.getBackground());
            setForeground(list.getForeground());
        }

        if (value instanceof Icon) {
            setIcon((Icon)value);
            setText("");
        }
        else {
            setIcon(null);
            setText((value == null) ? "" : value.toString());
        }

        if (list.getName() == null || !list.getName().equals("ComboBox.list")
                || !(list.getUI() instanceof SynthListUI)) {
            setEnabled(list.isEnabled());
        }

        setFont(list.getFont());

        Border border = null;
        if (cellHasFocus) {
            if (isSelected) {
                border = DefaultLookup.getBorder(this, ui, "List.focusSelectedCellHighlightBorder");
            }
            if (border == null) {
                border = DefaultLookup.getBorder(this, ui, "List.focusCellHighlightBorder");
            }
        } else {
            border = getNoFocusBorder();
        }
        setBorder(border);

        return this;
    }

    /**
     * Overridden for performance reasons.
     * See the <a href="#override">Implementation Note</a>
     * for more information.
     *
     * @since 1.5
     * @return <code>true</code> if the background is completely opaque
     *         and differs from the JList's background;
     *         <code>false</code> otherwise
     */
    @Override
    public boolean isOpaque() {
        Color back = getBackground();
        Component p = getParent();
        if (p != null) {
            p = p.getParent();
        }
        // p should now be the JList.
        boolean colorMatch = (back != null) && (p != null) &&
            back.equals(p.getBackground()) &&
                        p.isOpaque();
        return !colorMatch && super.isOpaque();
    }

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void validate() {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    *
    * @since 1.5
    */
    @Override
    public void invalidate() {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    *
    * @since 1.5
    */
    @Override
    public void repaint() {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void revalidate() {}
   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void repaint(long tm, int x, int y, int width, int height) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void repaint(Rectangle r) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    protected void firePropertyChange(String propertyName, Object oldValue, Object newValue) {
        // Strings get interned...
        if (propertyName == "text"
            || ((SwingUtilities2.isScaleChanged(propertyName, oldValue, newValue)
                    || propertyName == "font" || propertyName == "foreground")
                && oldValue != newValue
                && getClientProperty(javax.swing.plaf.basic.BasicHTML.propertyKey) != null)) {

            super.firePropertyChange(propertyName, oldValue, newValue);
        }
    }

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, byte oldValue, byte newValue) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, char oldValue, char newValue) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, short oldValue, short newValue) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, int oldValue, int newValue) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, long oldValue, long newValue) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, float oldValue, float newValue) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, double oldValue, double newValue) {}

   /**
    * Overridden for performance reasons.
    * See the <a href="#override">Implementation Note</a>
    * for more information.
    */
    @Override
    public void firePropertyChange(String propertyName, boolean oldValue, boolean newValue) {}

    /**
     * A subclass of DefaultListCellRenderer that implements UIResource.
     * DefaultListCellRenderer doesn't implement UIResource
     * directly so that applications can safely override the
     * cellRenderer property with DefaultListCellRenderer subclasses.
     * <p>
     * <strong>Warning:</strong>
     * Serialized objects of this class will not be compatible with
     * future Swing releases. The current serialization support is
     * appropriate for short term storage or RMI between applications running
     * the same version of Swing.  As of 1.4, support for long term storage
     * of all JavaBeans
     * has been added to the <code>java.beans</code> package.
     * Please see {@link java.beans.XMLEncoder}.
     */
    @SuppressWarnings("serial") // Same-version serialization only
    public static class UIResource extends DefaultListCellRenderer
        implements javax.swing.plaf.UIResource
    {
        /**
         * Constructs a {@code UIResource}.
         */
        public UIResource() {}
    }
}