/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2020, by Object Refinery Limited and Contributors.
 *
 * Project Info:  http://www.jfree.org/jfreechart/index.html
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library 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 Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 * USA.
 *
 * [Oracle and Java are registered trademarks of Oracle and/or its affiliates. 
 * Other names may be trademarks of their respective owners.]
 *
 * ---------
 * Axis.java
 * ---------
 * (C) Copyright 2000-2020, by Object Refinery Limited and Contributors.
 *
 * Original Author:  David Gilbert (for Object Refinery Limited);
 * Contributor(s):   Bill Kelemen;
 *                   Nicolas Brodu;
 *                   Peter Kolb (patches 1934255 and 2603321);
 *                   Andrew Mickish (patch 1870189); 
 *
 */

package org.jfree.chart.axis;

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.Paint;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.Stroke;
import java.awt.font.TextLayout;
import java.awt.geom.AffineTransform;
import java.awt.geom.Line2D;
import java.awt.geom.Rectangle2D;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.text.AttributedString;
import java.util.Arrays;
import java.util.EventListener;
import java.util.List;
import java.util.Objects;

import javax.swing.event.EventListenerList;

import org.jfree.chart.entity.AxisEntity;
import org.jfree.chart.entity.EntityCollection;
import org.jfree.chart.event.AxisChangeEvent;
import org.jfree.chart.event.AxisChangeListener;
import org.jfree.chart.plot.Plot;
import org.jfree.chart.plot.PlotRenderingInfo;
import org.jfree.chart.text.AttributedStringUtils;
import org.jfree.chart.text.TextUtils;
import org.jfree.chart.ui.RectangleEdge;
import org.jfree.chart.ui.RectangleInsets;
import org.jfree.chart.ui.TextAnchor;
import org.jfree.chart.util.AttrStringUtils;
import org.jfree.chart.util.PaintUtils;
import org.jfree.chart.util.Args;
import org.jfree.chart.util.SerialUtils;

/**
 * The base class for all axes in JFreeChart.  Subclasses are divided into
 * those that display values ({@link ValueAxis}) and those that display
 * categories ({@link CategoryAxis}).
 */
public abstract class Axis implements Cloneable, Serializable {

    /** For serialization. */
    private static final long serialVersionUID = 7719289504573298271L;

    /** The default axis visibility ({@code true}). */
    public static final boolean DEFAULT_AXIS_VISIBLE = true;

    /** The default axis label font ({@code Font("SansSerif", Font.PLAIN, 12)}). */
    public static final Font DEFAULT_AXIS_LABEL_FONT = new Font(
            "SansSerif", Font.PLAIN, 12);

    /** The default axis label paint ({@code Color.BLACK}). */
    public static final Paint DEFAULT_AXIS_LABEL_PAINT = Color.BLACK;

    /** The default axis label insets ({@code RectangleInsets(3.0, 3.0, 3.0, 3.0)}). */
    public static final RectangleInsets DEFAULT_AXIS_LABEL_INSETS
            = new RectangleInsets(3.0, 3.0, 3.0, 3.0);

    /** The default axis line paint ({@code Color.GRAY}). */
    public static final Paint DEFAULT_AXIS_LINE_PAINT = Color.GRAY;

    /** The default axis line stroke ({@code BasicStroke(0.5f)}). */
    public static final Stroke DEFAULT_AXIS_LINE_STROKE = new BasicStroke(0.5f);

    /** The default tick labels visibility ({@code true}). */
    public static final boolean DEFAULT_TICK_LABELS_VISIBLE = true;

    /** The default tick label font ({@code Font("SansSerif", Font.PLAIN, 10)}). */
    public static final Font DEFAULT_TICK_LABEL_FONT = new Font("SansSerif",
            Font.PLAIN, 10);

    /** The default tick label paint ({@code Color.BLACK}). */
    public static final Paint DEFAULT_TICK_LABEL_PAINT = Color.BLACK;

    /** The default tick label insets ({@code RectangleInsets(2.0, 4.0, 2.0, 4.0)}). */
    public static final RectangleInsets DEFAULT_TICK_LABEL_INSETS
            = new RectangleInsets(2.0, 4.0, 2.0, 4.0);

    /** The default tick marks visible ({@code true}). */
    public static final boolean DEFAULT_TICK_MARKS_VISIBLE = true;

    /** The default tick stroke ({@code BasicStroke(0.5f)}). */
    public static final Stroke DEFAULT_TICK_MARK_STROKE = new BasicStroke(0.5f);

    /** The default tick paint ({@code Color.GRAY}). */
    public static final Paint DEFAULT_TICK_MARK_PAINT = Color.GRAY;

    /** The default tick mark inside length ({@code 0.0f}). */
    public static final float DEFAULT_TICK_MARK_INSIDE_LENGTH = 0.0f;

    /** The default tick mark outside length ({@code 2.0f}). */
    public static final float DEFAULT_TICK_MARK_OUTSIDE_LENGTH = 2.0f;

    /** A flag indicating whether or not the axis is visible. */
    private boolean visible;

    /** The label for the axis. */
    private String label;
    
    /** 
     * An attributed label for the axis (overrides label if non-null).
     * We have to use this override method to preserve the API compatibility.
     */
    private transient AttributedString attributedLabel;

    /** The font for displaying the axis label. */
    private Font labelFont;

    /** The paint for drawing the axis label. */
    private transient Paint labelPaint;

    /** The insets for the axis label. */
    private RectangleInsets labelInsets;

    /** The label angle. */
    private double labelAngle;
    
    /** The axis label location (new in 1.0.16). */
    private AxisLabelLocation labelLocation;

    /** A flag that controls whether or not the axis line is visible. */
    private boolean axisLineVisible;

    /** The stroke used for the axis line. */
    private transient Stroke axisLineStroke;

    /** The paint used for the axis line. */
    private transient Paint axisLinePaint;

    /**
     * A flag that indicates whether or not tick labels are visible for the
     * axis.
     */
    private boolean tickLabelsVisible;

    /** The font used to display the tick labels. */
    private Font tickLabelFont;

    /** The color used to display the tick labels. */
    private transient Paint tickLabelPaint;

    /** The blank space around each tick label. */
    private RectangleInsets tickLabelInsets;

    /**
     * A flag that indicates whether or not major tick marks are visible for
     * the axis.
     */
    private boolean tickMarksVisible;

    /**
     * The length of the major tick mark inside the data area (zero
     * permitted).
     */
    private float tickMarkInsideLength;

    /**
     * The length of the major tick mark outside the data area (zero
     * permitted).
     */
    private float tickMarkOutsideLength;

    /**
     * A flag that indicates whether or not minor tick marks are visible for the
     * axis.
     *
     * @since 1.0.12
     */
    private boolean minorTickMarksVisible;

    /**
     * The length of the minor tick mark inside the data area (zero permitted).
     *
     * @since 1.0.12
     */
    private float minorTickMarkInsideLength;

    /**
     * The length of the minor tick mark outside the data area (zero permitted).
     *
     * @since 1.0.12
     */
    private float minorTickMarkOutsideLength;

    /** The stroke used to draw tick marks. */
    private transient Stroke tickMarkStroke;

    /** The paint used to draw tick marks. */
    private transient Paint tickMarkPaint;

    /** The fixed (horizontal or vertical) dimension for the axis. */
    private double fixedDimension;

    /**
     * A reference back to the plot that the axis is assigned to (can be
     * {@code null}).
     */
    private transient Plot plot;

    /** Storage for registered listeners. */
    private transient EventListenerList listenerList;

    /**
     * Constructs an axis with the specific label and default values for other
     * attributes.  
     *
     * @param label  the axis label ({@code null} permitted).
     */
    protected Axis(String label) {

        this.label = label;
        this.visible = DEFAULT_AXIS_VISIBLE;
        this.labelFont = DEFAULT_AXIS_LABEL_FONT;
        this.labelPaint = DEFAULT_AXIS_LABEL_PAINT;
        this.labelInsets = DEFAULT_AXIS_LABEL_INSETS;
        this.labelAngle = 0.0;
        this.labelLocation = AxisLabelLocation.MIDDLE;

        this.axisLineVisible = true;
        this.axisLinePaint = DEFAULT_AXIS_LINE_PAINT;
        this.axisLineStroke = DEFAULT_AXIS_LINE_STROKE;

        this.tickLabelsVisible = DEFAULT_TICK_LABELS_VISIBLE;
        this.tickLabelFont = DEFAULT_TICK_LABEL_FONT;
        this.tickLabelPaint = DEFAULT_TICK_LABEL_PAINT;
        this.tickLabelInsets = DEFAULT_TICK_LABEL_INSETS;

        this.tickMarksVisible = DEFAULT_TICK_MARKS_VISIBLE;
        this.tickMarkStroke = DEFAULT_TICK_MARK_STROKE;
        this.tickMarkPaint = DEFAULT_TICK_MARK_PAINT;
        this.tickMarkInsideLength = DEFAULT_TICK_MARK_INSIDE_LENGTH;
        this.tickMarkOutsideLength = DEFAULT_TICK_MARK_OUTSIDE_LENGTH;

        this.minorTickMarksVisible = false;
        this.minorTickMarkInsideLength = 0.0f;
        this.minorTickMarkOutsideLength = 2.0f;

        this.plot = null;

        this.listenerList = new EventListenerList();
    }

    /**
     * Returns {@code true} if the axis is visible, and
     * {@code false} otherwise.
     *
     * @return A boolean.
     *
     * @see #setVisible(boolean)
     */
    public boolean isVisible() {
        return this.visible;
    }

    /**
     * Sets a flag that controls whether or not the axis is visible and sends
     * an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param flag  the flag.
     *
     * @see #isVisible()
     */
    public void setVisible(boolean flag) {
        if (flag != this.visible) {
            this.visible = flag;
            fireChangeEvent();
        }
    }

    /**
     * Returns the label for the axis.
     *
     * @return The label for the axis ({@code null} possible).
     *
     * @see #getLabelFont()
     * @see #getLabelPaint()
     * @see #setLabel(String)
     */
    public String getLabel() {
        return this.label;
    }

    /**
     * Sets the label for the axis and sends an {@link AxisChangeEvent} to all
     * registered listeners.
     *
     * @param label  the new label ({@code null} permitted).
     *
     * @see #getLabel()
     * @see #setLabelFont(Font)
     * @see #setLabelPaint(Paint)
     */
    public void setLabel(String label) {
        this.label = label;
        fireChangeEvent();
    }

    /**
     * Returns the attributed label (the returned value is a copy, so 
     * modifying it will not impact the state of the axis).  The default value 
     * is {@code null}.
     * 
     * @return The attributed label (possibly {@code null}).
     * 
     * @since 1.0.16
     */
    public AttributedString getAttributedLabel() {
        if (this.attributedLabel != null) {
            return new AttributedString(this.attributedLabel.getIterator());
        } else {
            return null;
        }
    }
    
    /**
     * Sets the attributed label for the axis and sends an 
     * {@link AxisChangeEvent} to all registered listeners.  This is a 
     * convenience method that converts the string into an 
     * {@code AttributedString} using the current font attributes.
     * 
     * @param label  the label ({@code null} permitted).
     * 
     * @since 1.0.16
     */
    public void setAttributedLabel(String label) {
        setAttributedLabel(createAttributedLabel(label));    
    }
    
    /**
     * Sets the attributed label for the axis and sends an 
     * {@link AxisChangeEvent} to all registered listeners.
     * 
     * @param label  the label ({@code null} permitted).
     * 
     * @since 1.0.16
     */
    public void setAttributedLabel(AttributedString label) {
        if (label != null) {
            this.attributedLabel = new AttributedString(label.getIterator());
        } else {
            this.attributedLabel = null;
        }
        fireChangeEvent();
    }
    
    /**
     * Creates and returns an {@code AttributedString} with the specified
     * text and the labelFont and labelPaint applied as attributes.
     * 
     * @param label  the label ({@code null} permitted).
     * 
     * @return An attributed string or {@code null}.
     * 
     * @since 1.0.16
     */
    public AttributedString createAttributedLabel(String label) {
        if (label == null) {
            return null;
        }
        AttributedString s = new AttributedString(label);
        s.addAttributes(this.labelFont.getAttributes(), 0, label.length());
        return s;
    }
    
    /**
     * Returns the font for the axis label.
     *
     * @return The font (never {@code null}).
     *
     * @see #setLabelFont(Font)
     */
    public Font getLabelFont() {
        return this.labelFont;
    }

    /**
     * Sets the font for the axis label and sends an {@link AxisChangeEvent}
     * to all registered listeners.
     *
     * @param font  the font ({@code null} not permitted).
     *
     * @see #getLabelFont()
     */
    public void setLabelFont(Font font) {
        Args.nullNotPermitted(font, "font");
        if (!this.labelFont.equals(font)) {
            this.labelFont = font;
            fireChangeEvent();
        }
    }

    /**
     * Returns the color/shade used to draw the axis label.
     *
     * @return The paint (never {@code null}).
     *
     * @see #setLabelPaint(Paint)
     */
    public Paint getLabelPaint() {
        return this.labelPaint;
    }

    /**
     * Sets the paint used to draw the axis label and sends an
     * {@link AxisChangeEvent} to all registered listeners.
     *
     * @param paint  the paint ({@code null} not permitted).
     *
     * @see #getLabelPaint()
     */
    public void setLabelPaint(Paint paint) {
        Args.nullNotPermitted(paint, "paint");
        this.labelPaint = paint;
        fireChangeEvent();
    }

    /**
     * Returns the insets for the label (that is, the amount of blank space
     * that should be left around the label).
     *
     * @return The label insets (never {@code null}).
     *
     * @see #setLabelInsets(RectangleInsets)
     */
    public RectangleInsets getLabelInsets() {
        return this.labelInsets;
    }

    /**
     * Sets the insets for the axis label, and sends an {@link AxisChangeEvent}
     * to all registered listeners.
     *
     * @param insets  the insets ({@code null} not permitted).
     *
     * @see #getLabelInsets()
     */
    public void setLabelInsets(RectangleInsets insets) {
        setLabelInsets(insets, true);
    }

    /**
     * Sets the insets for the axis label, and sends an {@link AxisChangeEvent}
     * to all registered listeners.
     *
     * @param insets  the insets ({@code null} not permitted).
     * @param notify  notify listeners?
     *
     * @since 1.0.10
     */
    public void setLabelInsets(RectangleInsets insets, boolean notify) {
        Args.nullNotPermitted(insets, "insets");
        if (!insets.equals(this.labelInsets)) {
            this.labelInsets = insets;
            if (notify) {
                fireChangeEvent();
            }
        }
    }

    /**
     * Returns the angle of the axis label.
     *
     * @return The angle (in radians).
     *
     * @see #setLabelAngle(double)
     */
    public double getLabelAngle() {
        return this.labelAngle;
    }

    /**
     * Sets the angle for the label and sends an {@link AxisChangeEvent} to all
     * registered listeners.
     *
     * @param angle  the angle (in radians).
     *
     * @see #getLabelAngle()
     */
    public void setLabelAngle(double angle) {
        this.labelAngle = angle;
        fireChangeEvent();
    }
    
    /**
     * Returns the location of the axis label.  The default is
     * {@link AxisLabelLocation#MIDDLE}.
     * 
     * @return The location of the axis label (never {@code null}). 
     * 
     * @since 1.0.16
     */
    public AxisLabelLocation getLabelLocation() {
        return this.labelLocation;
    }
    
    /**
     * Sets the axis label location and sends an {@link AxisChangeEvent} to
     * all registered listeners.
     * 
     * @param location  the new location ({@code null} not permitted).
     * 
     * @since 1.0.16
     */
    public void setLabelLocation(AxisLabelLocation location) {
        Args.nullNotPermitted(location, "location");
        this.labelLocation = location;
        fireChangeEvent();
    }

    /**
     * A flag that controls whether or not the axis line is drawn.
     *
     * @return A boolean.
     *
     * @see #getAxisLinePaint()
     * @see #getAxisLineStroke()
     * @see #setAxisLineVisible(boolean)
     */
    public boolean isAxisLineVisible() {
        return this.axisLineVisible;
    }

    /**
     * Sets a flag that controls whether or not the axis line is visible and
     * sends an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param visible  the flag.
     *
     * @see #isAxisLineVisible()
     * @see #setAxisLinePaint(Paint)
     * @see #setAxisLineStroke(Stroke)
     */
    public void setAxisLineVisible(boolean visible) {
        this.axisLineVisible = visible;
        fireChangeEvent();
    }

    /**
     * Returns the paint used to draw the axis line.
     *
     * @return The paint (never {@code null}).
     *
     * @see #setAxisLinePaint(Paint)
     */
    public Paint getAxisLinePaint() {
        return this.axisLinePaint;
    }

    /**
     * Sets the paint used to draw the axis line and sends an
     * {@link AxisChangeEvent} to all registered listeners.
     *
     * @param paint  the paint ({@code null} not permitted).
     *
     * @see #getAxisLinePaint()
     */
    public void setAxisLinePaint(Paint paint) {
        Args.nullNotPermitted(paint, "paint");
        this.axisLinePaint = paint;
        fireChangeEvent();
    }

    /**
     * Returns the stroke used to draw the axis line.
     *
     * @return The stroke (never {@code null}).
     *
     * @see #setAxisLineStroke(Stroke)
     */
    public Stroke getAxisLineStroke() {
        return this.axisLineStroke;
    }

    /**
     * Sets the stroke used to draw the axis line and sends an
     * {@link AxisChangeEvent} to all registered listeners.
     *
     * @param stroke  the stroke ({@code null} not permitted).
     *
     * @see #getAxisLineStroke()
     */
    public void setAxisLineStroke(Stroke stroke) {
        Args.nullNotPermitted(stroke, "stroke");
        this.axisLineStroke = stroke;
        fireChangeEvent();
    }

    /**
     * Returns a flag indicating whether or not the tick labels are visible.
     *
     * @return The flag.
     *
     * @see #getTickLabelFont()
     * @see #getTickLabelPaint()
     * @see #setTickLabelsVisible(boolean)
     */
    public boolean isTickLabelsVisible() {
        return this.tickLabelsVisible;
    }

    /**
     * Sets the flag that determines whether or not the tick labels are
     * visible and sends an {@link AxisChangeEvent} to all registered
     * listeners.
     *
     * @param flag  the flag.
     *
     * @see #isTickLabelsVisible()
     * @see #setTickLabelFont(Font)
     * @see #setTickLabelPaint(Paint)
     */
    public void setTickLabelsVisible(boolean flag) {

        if (flag != this.tickLabelsVisible) {
            this.tickLabelsVisible = flag;
            fireChangeEvent();
        }

    }

    /**
     * Returns the flag that indicates whether or not the minor tick marks are
     * showing.
     *
     * @return The flag that indicates whether or not the minor tick marks are
     *         showing.
     *
     * @see #setMinorTickMarksVisible(boolean)
     *
     * @since 1.0.12
     */
    public boolean isMinorTickMarksVisible() {
        return this.minorTickMarksVisible;
    }

    /**
     * Sets the flag that indicates whether or not the minor tick marks are 
     * showing and sends an {@link AxisChangeEvent} to all registered
     * listeners.
     *
     * @param flag  the flag.
     *
     * @see #isMinorTickMarksVisible()
     *
     * @since 1.0.12
     */
    public void setMinorTickMarksVisible(boolean flag) {
        if (flag != this.minorTickMarksVisible) {
            this.minorTickMarksVisible = flag;
            fireChangeEvent();
        }
    }

    /**
     * Returns the font used for the tick labels (if showing).
     *
     * @return The font (never {@code null}).
     *
     * @see #setTickLabelFont(Font)
     */
    public Font getTickLabelFont() {
        return this.tickLabelFont;
    }

    /**
     * Sets the font for the tick labels and sends an {@link AxisChangeEvent}
     * to all registered listeners.
     *
     * @param font  the font ({@code null} not allowed).
     *
     * @see #getTickLabelFont()
     */
    public void setTickLabelFont(Font font) {
        Args.nullNotPermitted(font, "font");
        if (!this.tickLabelFont.equals(font)) {
            this.tickLabelFont = font;
            fireChangeEvent();
        }
    }

    /**
     * Returns the color/shade used for the tick labels.
     *
     * @return The paint used for the tick labels.
     *
     * @see #setTickLabelPaint(Paint)
     */
    public Paint getTickLabelPaint() {
        return this.tickLabelPaint;
    }

    /**
     * Sets the paint used to draw tick labels (if they are showing) and
     * sends an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param paint  the paint ({@code null} not permitted).
     *
     * @see #getTickLabelPaint()
     */
    public void setTickLabelPaint(Paint paint) {
        Args.nullNotPermitted(paint, "paint");
        this.tickLabelPaint = paint;
        fireChangeEvent();
    }

    /**
     * Returns the insets for the tick labels.
     *
     * @return The insets (never {@code null}).
     *
     * @see #setTickLabelInsets(RectangleInsets)
     */
    public RectangleInsets getTickLabelInsets() {
        return this.tickLabelInsets;
    }

    /**
     * Sets the insets for the tick labels and sends an {@link AxisChangeEvent}
     * to all registered listeners.
     *
     * @param insets  the insets ({@code null} not permitted).
     *
     * @see #getTickLabelInsets()
     */
    public void setTickLabelInsets(RectangleInsets insets) {
        Args.nullNotPermitted(insets, "insets");
        if (!this.tickLabelInsets.equals(insets)) {
            this.tickLabelInsets = insets;
            fireChangeEvent();
        }
    }

    /**
     * Returns the flag that indicates whether or not the tick marks are
     * showing.
     *
     * @return The flag that indicates whether or not the tick marks are
     *         showing.
     *
     * @see #setTickMarksVisible(boolean)
     */
    public boolean isTickMarksVisible() {
        return this.tickMarksVisible;
    }

    /**
     * Sets the flag that indicates whether or not the tick marks are showing
     * and sends an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param flag  the flag.
     *
     * @see #isTickMarksVisible()
     */
    public void setTickMarksVisible(boolean flag) {
        if (flag != this.tickMarksVisible) {
            this.tickMarksVisible = flag;
            fireChangeEvent();
        }
    }

    /**
     * Returns the inside length of the tick marks.
     *
     * @return The length.
     *
     * @see #getTickMarkOutsideLength()
     * @see #setTickMarkInsideLength(float)
     */
    public float getTickMarkInsideLength() {
        return this.tickMarkInsideLength;
    }

    /**
     * Sets the inside length of the tick marks and sends
     * an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param length  the new length.
     *
     * @see #getTickMarkInsideLength()
     */
    public void setTickMarkInsideLength(float length) {
        this.tickMarkInsideLength = length;
        fireChangeEvent();
    }

    /**
     * Returns the outside length of the tick marks.
     *
     * @return The length.
     *
     * @see #getTickMarkInsideLength()
     * @see #setTickMarkOutsideLength(float)
     */
    public float getTickMarkOutsideLength() {
        return this.tickMarkOutsideLength;
    }

    /**
     * Sets the outside length of the tick marks and sends
     * an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param length  the new length.
     *
     * @see #getTickMarkInsideLength()
     */
    public void setTickMarkOutsideLength(float length) {
        this.tickMarkOutsideLength = length;
        fireChangeEvent();
    }

    /**
     * Returns the stroke used to draw tick marks.
     *
     * @return The stroke (never {@code null}).
     *
     * @see #setTickMarkStroke(Stroke)
     */
    public Stroke getTickMarkStroke() {
        return this.tickMarkStroke;
    }

    /**
     * Sets the stroke used to draw tick marks and sends
     * an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param stroke  the stroke ({@code null} not permitted).
     *
     * @see #getTickMarkStroke()
     */
    public void setTickMarkStroke(Stroke stroke) {
        Args.nullNotPermitted(stroke, "stroke");
        if (!this.tickMarkStroke.equals(stroke)) {
            this.tickMarkStroke = stroke;
            fireChangeEvent();
        }
    }

    /**
     * Returns the paint used to draw tick marks (if they are showing).
     *
     * @return The paint (never {@code null}).
     *
     * @see #setTickMarkPaint(Paint)
     */
    public Paint getTickMarkPaint() {
        return this.tickMarkPaint;
    }

    /**
     * Sets the paint used to draw tick marks and sends an
     * {@link AxisChangeEvent} to all registered listeners.
     *
     * @param paint  the paint ({@code null} not permitted).
     *
     * @see #getTickMarkPaint()
     */
    public void setTickMarkPaint(Paint paint) {
        Args.nullNotPermitted(paint, "paint");
        this.tickMarkPaint = paint;
        fireChangeEvent();
    }

    /**
     * Returns the inside length of the minor tick marks.
     *
     * @return The length.
     *
     * @see #getMinorTickMarkOutsideLength()
     * @see #setMinorTickMarkInsideLength(float)
     *
     * @since 1.0.12
     */
    public float getMinorTickMarkInsideLength() {
        return this.minorTickMarkInsideLength;
    }

    /**
     * Sets the inside length of the minor tick marks and sends
     * an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param length  the new length.
     *
     * @see #getMinorTickMarkInsideLength()
     *
     * @since 1.0.12
     */
    public void setMinorTickMarkInsideLength(float length) {
        this.minorTickMarkInsideLength = length;
        fireChangeEvent();
    }

    /**
     * Returns the outside length of the minor tick marks.
     *
     * @return The length.
     *
     * @see #getMinorTickMarkInsideLength()
     * @see #setMinorTickMarkOutsideLength(float)
     *
     * @since 1.0.12
     */
    public float getMinorTickMarkOutsideLength() {
        return this.minorTickMarkOutsideLength;
    }

    /**
     * Sets the outside length of the minor tick marks and sends
     * an {@link AxisChangeEvent} to all registered listeners.
     *
     * @param length  the new length.
     *
     * @see #getMinorTickMarkInsideLength()
     *
     * @since 1.0.12
     */
    public void setMinorTickMarkOutsideLength(float length) {
        this.minorTickMarkOutsideLength = length;
        fireChangeEvent();
    }

    /**
     * Returns the plot that the axis is assigned to.  This method will return
     * {@code null} if the axis is not currently assigned to a plot.
     *
     * @return The plot that the axis is assigned to (possibly {@code null}).
     *
     * @see #setPlot(Plot)
     */
    public Plot getPlot() {
        return this.plot;
    }

    /**
     * Sets a reference to the plot that the axis is assigned to.
     * <P>
     * This method is used internally, you shouldn't need to call it yourself.
     *
     * @param plot  the plot.
     *
     * @see #getPlot()
     */
    public void setPlot(Plot plot) {
        this.plot = plot;
        configure();
    }

    /**
     * Returns the fixed dimension for the axis.
     *
     * @return The fixed dimension.
     *
     * @see #setFixedDimension(double)
     */
    public double getFixedDimension() {
        return this.fixedDimension;
    }

    /**
     * Sets the fixed dimension for the axis.
     * <P>
     * This is used when combining more than one plot on a chart.  In this case,
     * there may be several axes that need to have the same height or width so
     * that they are aligned.  This method is used to fix a dimension for the
     * axis (the context determines whether the dimension is horizontal or
     * vertical).
     *
     * @param dimension  the fixed dimension.
     *
     * @see #getFixedDimension()
     */
    public void setFixedDimension(double dimension) {
        this.fixedDimension = dimension;
    }

    /**
     * Configures the axis to work with the current plot.  Override this method
     * to perform any special processing (such as auto-rescaling).
     */
    public abstract void configure();

    /**
     * Estimates the space (height or width) required to draw the axis.
     *
     * @param g2  the graphics device.
     * @param plot  the plot that the axis belongs to.
     * @param plotArea  the area within which the plot (including axes) should
     *                  be drawn.
     * @param edge  the axis location.
     * @param space  space already reserved.
     *
     * @return The space required to draw the axis (including pre-reserved
     *         space).
     */
    public abstract AxisSpace reserveSpace(Graphics2D g2, Plot plot,
                                           Rectangle2D plotArea,
                                           RectangleEdge edge,
                                           AxisSpace space);

    /**
     * Draws the axis on a Java 2D graphics device (such as the screen or a
     * printer).
     *
     * @param g2  the graphics device ({@code null} not permitted).
     * @param cursor  the cursor location (determines where to draw the axis).
     * @param plotArea  the area within which the axes and plot should be drawn.
     * @param dataArea  the area within which the data should be drawn.
     * @param edge  the axis location ({@code null} not permitted).
     * @param plotState  collects information about the plot
     *                   ({@code null} permitted).
     *
     * @return The axis state (never {@code null}).
     */
    public abstract AxisState draw(Graphics2D g2, double cursor,
            Rectangle2D plotArea, Rectangle2D dataArea, RectangleEdge edge,
            PlotRenderingInfo plotState);

    /**
     * Calculates the positions of the ticks for the axis, storing the results
     * in the tick list (ready for drawing).
     *
     * @param g2  the graphics device.
     * @param state  the axis state.
     * @param dataArea  the area inside the axes.
     * @param edge  the edge on which the axis is located.
     *
     * @return The list of ticks.
     */
    public abstract List refreshTicks(Graphics2D g2, AxisState state,
            Rectangle2D dataArea, RectangleEdge edge);

    /**
     * Creates an entity for the axis and adds it to the rendering info.
     * If {@code plotState} is {@code null}, this means that rendering info
     * is not being collected so this method simply returns without doing 
     * anything.
     * 
     * @param cursor  the initial cursor value.
     * @param state  the axis state after completion of the drawing with a
     *     possibly updated cursor position.
     * @param dataArea  the data area.
     * @param edge  the edge ({@code null} not permitted).
     * @param plotState  the PlotRenderingInfo from which a reference to the
     *     entity collection can be obtained ({@code null} permitted).
     *
     * @since 1.0.13
     */
    protected void createAndAddEntity(double cursor, AxisState state,
            Rectangle2D dataArea, RectangleEdge edge,
            PlotRenderingInfo plotState) {

        Args.nullNotPermitted(edge, "edge");
        if (plotState == null || plotState.getOwner() == null) {
            return;  // no need to create entity if we can't save it anyways...
        }
        Rectangle2D hotspot = null;
        if (edge.equals(RectangleEdge.TOP)) {
            hotspot = new Rectangle2D.Double(dataArea.getX(),
                    state.getCursor(), dataArea.getWidth(),
                    cursor - state.getCursor());
        }
        else if (edge.equals(RectangleEdge.BOTTOM)) {
            hotspot = new Rectangle2D.Double(dataArea.getX(), cursor,
                    dataArea.getWidth(), state.getCursor() - cursor);
        }
        else if (edge.equals(RectangleEdge.LEFT)) {
            hotspot = new Rectangle2D.Double(state.getCursor(),
                    dataArea.getY(), cursor - state.getCursor(),
                    dataArea.getHeight());
        }
        else if (edge.equals(RectangleEdge.RIGHT)) {
            hotspot = new Rectangle2D.Double(cursor, dataArea.getY(),
                    state.getCursor() - cursor, dataArea.getHeight());
        }
        EntityCollection e = plotState.getOwner().getEntityCollection();
        if (e != null) {
            e.add(new AxisEntity(hotspot, this));
        }
    }

    /**
     * Registers an object for notification of changes to the axis.
     *
     * @param listener  the object that is being registered.
     *
     * @see #removeChangeListener(AxisChangeListener)
     */
    public void addChangeListener(AxisChangeListener listener) {
        this.listenerList.add(AxisChangeListener.class, listener);
    }

    /**
     * Deregisters an object for notification of changes to the axis.
     *
     * @param listener  the object to deregister.
     *
     * @see #addChangeListener(AxisChangeListener)
     */
    public void removeChangeListener(AxisChangeListener listener) {
        this.listenerList.remove(AxisChangeListener.class, listener);
    }

    /**
     * Returns {@code true} if the specified object is registered with
     * the dataset as a listener.  Most applications won't need to call this
     * method, it exists mainly for use by unit testing code.
     *
     * @param listener  the listener.
     *
     * @return A boolean.
     */
    public boolean hasListener(EventListener listener) {
        List list = Arrays.asList(this.listenerList.getListenerList());
        return list.contains(listener);
    }

    /**
     * Notifies all registered listeners that the axis has changed.
     * The AxisChangeEvent provides information about the change.
     *
     * @param event  information about the change to the axis.
     */
    protected void notifyListeners(AxisChangeEvent event) {
        Object[] listeners = this.listenerList.getListenerList();
        for (int i = listeners.length - 2; i >= 0; i -= 2) {
            if (listeners[i] == AxisChangeListener.class) {
                ((AxisChangeListener) listeners[i + 1]).axisChanged(event);
            }
        }
    }

    /**
     * Sends an {@link AxisChangeEvent} to all registered listeners.
     *
     * @since 1.0.12
     */
    protected void fireChangeEvent() {
        notifyListeners(new AxisChangeEvent(this));
    }

    /**
     * Returns a rectangle that encloses the axis label.  This is typically
     * used for layout purposes (it gives the maximum dimensions of the label).
     *
     * @param g2  the graphics device.
     * @param edge  the edge of the plot area along which the axis is measuring.
     *
     * @return The enclosing rectangle.
     */
    protected Rectangle2D getLabelEnclosure(Graphics2D g2, RectangleEdge edge) {
        Rectangle2D result = new Rectangle2D.Double();
        Rectangle2D bounds = null;
        if (this.attributedLabel != null) {
            TextLayout layout = new TextLayout(
                    this.attributedLabel.getIterator(), 
                    g2.getFontRenderContext());
            bounds = layout.getBounds();
        } else {
            String axisLabel = getLabel();
            if (axisLabel != null && !axisLabel.equals("")) {
                FontMetrics fm = g2.getFontMetrics(getLabelFont());
                bounds = TextUtils.getTextBounds(axisLabel, g2, fm);
            }
        }
        if (bounds != null) {
            RectangleInsets insets = getLabelInsets();
            bounds = insets.createOutsetRectangle(bounds);
            double angle = getLabelAngle();
            if (edge == RectangleEdge.LEFT || edge == RectangleEdge.RIGHT) {
                angle = angle - Math.PI / 2.0;
            }
            double x = bounds.getCenterX();
            double y = bounds.getCenterY();
            AffineTransform transformer
                = AffineTransform.getRotateInstance(angle, x, y);
            Shape labelBounds = transformer.createTransformedShape(bounds);
            result = labelBounds.getBounds2D();
        }
        return result;
    }

    /**
     * Returns the x-coordinate for the point to which the axis label should 
     * be aligned.
     * 
     * @param location  the axis label location ({@code null} not permitted).
     * @param dataArea  the display area in which the data will be rendered ({@code null} not permitted).
     * 
     * @return The x-coordinate. 
     */
    protected double labelLocationX(AxisLabelLocation location, 
            Rectangle2D dataArea) {
        if (location.equals(AxisLabelLocation.HIGH_END)) {
            return dataArea.getMaxX();
        }
        if (location.equals(AxisLabelLocation.MIDDLE)) {
            return dataArea.getCenterX();
        }
        if (location.equals(AxisLabelLocation.LOW_END)) {
            return dataArea.getMinX();
        }
        throw new RuntimeException("Unexpected AxisLabelLocation: " + location);
    }
    
    /**
     * Returns the y-coordinate for the point to which the axis label should
     * be aligned.
     * 
     * @param location  the location ({@code null} not permitted).
     * @param dataArea  the data area ({@code null} not permitted).
     * 
     * @return The y-coordinate. 
     */
    protected double labelLocationY(AxisLabelLocation location, 
            Rectangle2D dataArea) {
        if (location.equals(AxisLabelLocation.HIGH_END)) {
            return dataArea.getMinY();
        }
        if (location.equals(AxisLabelLocation.MIDDLE)) {
            return dataArea.getCenterY();
        }
        if (location.equals(AxisLabelLocation.LOW_END)) {
            return dataArea.getMaxY();
        }
        throw new RuntimeException("Unexpected AxisLabelLocation: " + location);
    }
    
    /**
     * Returns the appropriate horizontal text anchor for the specified axis 
     * location.
     * 
     * @param location  the location ({@code null} not permitted).
     * 
     * @return The text anchor (never {@code null}). 
     */
    protected TextAnchor labelAnchorH(AxisLabelLocation location) {
        if (location.equals(AxisLabelLocation.HIGH_END)) {
            return TextAnchor.CENTER_RIGHT;
        }
        if (location.equals(AxisLabelLocation.MIDDLE)) {
            return TextAnchor.CENTER;
        }
        if (location.equals(AxisLabelLocation.LOW_END)) {
            return TextAnchor.CENTER_LEFT;
        }
        throw new RuntimeException("Unexpected AxisLabelLocation: " + location);
    }
    
    /**
     * Returns the appropriate vertical text anchor for the specified axis 
     * location.
     * 
     * @param location  the location ({@code null} not permitted).
     * 
     * @return The text anchor (never {@code null}). 
     */
    protected TextAnchor labelAnchorV(AxisLabelLocation location) {
        if (location.equals(AxisLabelLocation.HIGH_END)) {
            return TextAnchor.CENTER_RIGHT;
        }
        if (location.equals(AxisLabelLocation.MIDDLE)) {
            return TextAnchor.CENTER;
        }
        if (location.equals(AxisLabelLocation.LOW_END)) {
            return TextAnchor.CENTER_LEFT;
        }
        throw new RuntimeException("Unexpected AxisLabelLocation: " + location);
    }

    /**
     * Draws the axis label.
     *
     * @param label  the label text.
     * @param g2  the graphics device.
     * @param plotArea  the plot area.
     * @param dataArea  the area inside the axes.
     * @param edge  the location of the axis.
     * @param state  the axis state ({@code null} not permitted).
     *
     * @return Information about the axis.
     */
    protected AxisState drawLabel(String label, Graphics2D g2,
            Rectangle2D plotArea, Rectangle2D dataArea, RectangleEdge edge,
            AxisState state) {

        // it is unlikely that 'state' will be null, but check anyway...
        Args.nullNotPermitted(state, "state");

        if ((label == null) || (label.equals(""))) {
            return state;
        }

        Font font = getLabelFont();
        RectangleInsets insets = getLabelInsets();
        g2.setFont(font);
        g2.setPaint(getLabelPaint());
        FontMetrics fm = g2.getFontMetrics();
        Rectangle2D labelBounds = TextUtils.getTextBounds(label, g2, fm);

        if (edge == RectangleEdge.TOP) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle(), labelBounds.getCenterX(),
                    labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = labelLocationX(this.labelLocation, dataArea);
            double labely = state.getCursor() - insets.getBottom()
                            - labelBounds.getHeight() / 2.0;
            TextAnchor anchor = labelAnchorH(this.labelLocation);
            TextUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle(), TextAnchor.CENTER);
            state.cursorUp(insets.getTop() + labelBounds.getHeight()
                    + insets.getBottom());
        }
        else if (edge == RectangleEdge.BOTTOM) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle(), labelBounds.getCenterX(),
                    labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = labelLocationX(this.labelLocation, dataArea);
            double labely = state.getCursor()
                            + insets.getTop() + labelBounds.getHeight() / 2.0;
            TextAnchor anchor = labelAnchorH(this.labelLocation);
            TextUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle(), TextAnchor.CENTER);
            state.cursorDown(insets.getTop() + labelBounds.getHeight()
                    + insets.getBottom());
        }
        else if (edge == RectangleEdge.LEFT) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle() - Math.PI / 2.0, labelBounds.getCenterX(),
                    labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = state.getCursor()
                            - insets.getRight() - labelBounds.getWidth() / 2.0;
            double labely = labelLocationY(this.labelLocation, dataArea);
            TextAnchor anchor = labelAnchorV(this.labelLocation);
            TextUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle() - Math.PI / 2.0, 
                    anchor);
            state.cursorLeft(insets.getLeft() + labelBounds.getWidth()
                    + insets.getRight());
        }
        else if (edge == RectangleEdge.RIGHT) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle() + Math.PI / 2.0,
                    labelBounds.getCenterX(), labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = state.getCursor()
                            + insets.getLeft() + labelBounds.getWidth() / 2.0;
            double labely = labelLocationY(this.labelLocation, dataArea);
            TextAnchor anchor = labelAnchorV(this.labelLocation);
            TextUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle() + Math.PI / 2.0, 
                    anchor);
            state.cursorRight(insets.getLeft() + labelBounds.getWidth()
                    + insets.getRight());
        }

        return state;

    }

    /**
     * Draws the axis label.
     *
     * @param label  the label text.
     * @param g2  the graphics device.
     * @param plotArea  the plot area.
     * @param dataArea  the area inside the axes.
     * @param edge  the location of the axis.
     * @param state  the axis state ({@code null} not permitted).
     *
     * @return Information about the axis.
     * 
     * @since 1.0.16
     */
    protected AxisState drawAttributedLabel(AttributedString label, 
            Graphics2D g2, Rectangle2D plotArea, Rectangle2D dataArea, 
            RectangleEdge edge, AxisState state) {

        // it is unlikely that 'state' will be null, but check anyway...
        Args.nullNotPermitted(state, "state");

        if (label == null) {
            return state;
        }

        RectangleInsets insets = getLabelInsets();
        g2.setFont(getLabelFont());
        g2.setPaint(getLabelPaint());
        TextLayout layout = new TextLayout(this.attributedLabel.getIterator(),
                g2.getFontRenderContext());
        Rectangle2D labelBounds = layout.getBounds();

        if (edge == RectangleEdge.TOP) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle(), labelBounds.getCenterX(),
                    labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = labelLocationX(this.labelLocation, dataArea);
            double labely = state.getCursor() - insets.getBottom()
                            - labelBounds.getHeight() / 2.0;
            TextAnchor anchor = labelAnchorH(this.labelLocation);
            AttrStringUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle(), TextAnchor.CENTER);
            state.cursorUp(insets.getTop() + labelBounds.getHeight()
                    + insets.getBottom());
        }
        else if (edge == RectangleEdge.BOTTOM) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle(), labelBounds.getCenterX(),
                    labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = labelLocationX(this.labelLocation, dataArea);
            double labely = state.getCursor()
                            + insets.getTop() + labelBounds.getHeight() / 2.0;
            TextAnchor anchor = labelAnchorH(this.labelLocation);
            AttrStringUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle(), TextAnchor.CENTER);
            state.cursorDown(insets.getTop() + labelBounds.getHeight()
                    + insets.getBottom());
        }
        else if (edge == RectangleEdge.LEFT) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle() - Math.PI / 2.0, labelBounds.getCenterX(),
                    labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = state.getCursor()
                            - insets.getRight() - labelBounds.getWidth() / 2.0;
            double labely = labelLocationY(this.labelLocation, dataArea);
            TextAnchor anchor = labelAnchorV(this.labelLocation);
            AttrStringUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle() - Math.PI / 2.0, 
                    anchor);
            state.cursorLeft(insets.getLeft() + labelBounds.getWidth()
                    + insets.getRight());
        }
        else if (edge == RectangleEdge.RIGHT) {
            AffineTransform t = AffineTransform.getRotateInstance(
                    getLabelAngle() + Math.PI / 2.0,
                    labelBounds.getCenterX(), labelBounds.getCenterY());
            Shape rotatedLabelBounds = t.createTransformedShape(labelBounds);
            labelBounds = rotatedLabelBounds.getBounds2D();
            double labelx = state.getCursor()
                            + insets.getLeft() + labelBounds.getWidth() / 2.0;
            double labely = labelLocationY(this.labelLocation, dataArea);
            TextAnchor anchor = labelAnchorV(this.labelLocation);
            AttrStringUtils.drawRotatedString(label, g2, (float) labelx,
                    (float) labely, anchor, getLabelAngle() + Math.PI / 2.0, 
                    anchor);
            state.cursorRight(insets.getLeft() + labelBounds.getWidth()
                    + insets.getRight());
        }
        return state;
    }

    /**
     * Draws an axis line at the current cursor position and edge.
     *
     * @param g2  the graphics device.
     * @param cursor  the cursor position.
     * @param dataArea  the data area.
     * @param edge  the edge.
     */
    protected void drawAxisLine(Graphics2D g2, double cursor,
            Rectangle2D dataArea, RectangleEdge edge) {
        Line2D axisLine = null;
        double x = dataArea.getX();
        double y = dataArea.getY();
        if (edge == RectangleEdge.TOP) {
            axisLine = new Line2D.Double(x, cursor, dataArea.getMaxX(), cursor);
        } else if (edge == RectangleEdge.BOTTOM) {
            axisLine = new Line2D.Double(x, cursor, dataArea.getMaxX(), cursor);
        } else if (edge == RectangleEdge.LEFT) {
            axisLine = new Line2D.Double(cursor, y, cursor, dataArea.getMaxY());
        } else if (edge == RectangleEdge.RIGHT) {
            axisLine = new Line2D.Double(cursor, y, cursor, dataArea.getMaxY());
        }
        g2.setPaint(this.axisLinePaint);
        g2.setStroke(this.axisLineStroke);
        Object saved = g2.getRenderingHint(RenderingHints.KEY_STROKE_CONTROL);
        g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, 
                RenderingHints.VALUE_STROKE_NORMALIZE);
        g2.draw(axisLine);
        g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, saved);
    }

    /**
     * Returns a clone of the axis.
     *
     * @return A clone.
     *
     * @throws CloneNotSupportedException if some component of the axis does
     *         not support cloning.
     */
    @Override
    public Object clone() throws CloneNotSupportedException {
        Axis clone = (Axis) super.clone();
        // It's up to the plot which clones up to restore the correct references
        clone.plot = null;
        clone.listenerList = new EventListenerList();
        return clone;
    }

    /**
     * Tests this axis for equality with another object.
     *
     * @param obj  the object ({@code null} permitted).
     *
     * @return {@code true} or {@code false}.
     */
    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof Axis)) {
            return false;
        }
        Axis that = (Axis) obj;
        if (this.visible != that.visible) {
            return false;
        }
        if (!Objects.equals(this.label, that.label)) {
            return false;
        }
        if (!AttributedStringUtils.equal(this.attributedLabel, 
                that.attributedLabel)) {
            return false;
        }
        if (!Objects.equals(this.labelFont, that.labelFont)) {
            return false;
        }
        if (!PaintUtils.equal(this.labelPaint, that.labelPaint)) {
            return false;
        }
        if (!Objects.equals(this.labelInsets, that.labelInsets)) {
            return false;
        }
        if (this.labelAngle != that.labelAngle) {
            return false;
        }
        if (!this.labelLocation.equals(that.labelLocation)) {
            return false;
        }
        if (this.axisLineVisible != that.axisLineVisible) {
            return false;
        }
        if (!Objects.equals(this.axisLineStroke, that.axisLineStroke)) {
            return false;
        }
        if (!PaintUtils.equal(this.axisLinePaint, that.axisLinePaint)) {
            return false;
        }
        if (this.tickLabelsVisible != that.tickLabelsVisible) {
            return false;
        }
        if (!Objects.equals(this.tickLabelFont, that.tickLabelFont)) {
            return false;
        }
        if (!PaintUtils.equal(this.tickLabelPaint, that.tickLabelPaint)) {
            return false;
        }
        if (!Objects.equals(this.tickLabelInsets, that.tickLabelInsets)) {
            return false;
        }
        if (this.tickMarksVisible != that.tickMarksVisible) {
            return false;
        }
        if (this.tickMarkInsideLength != that.tickMarkInsideLength) {
            return false;
        }
        if (this.tickMarkOutsideLength != that.tickMarkOutsideLength) {
            return false;
        }
        if (!PaintUtils.equal(this.tickMarkPaint, that.tickMarkPaint)) {
            return false;
        }
        if (!Objects.equals(this.tickMarkStroke, that.tickMarkStroke)) {
            return false;
        }
        if (this.minorTickMarksVisible != that.minorTickMarksVisible) {
            return false;
        }
        if (this.minorTickMarkInsideLength != that.minorTickMarkInsideLength) {
            return false;
        }
        if (this.minorTickMarkOutsideLength
                != that.minorTickMarkOutsideLength) {
            return false;
        }
        if (this.fixedDimension != that.fixedDimension) {
            return false;
        }
        return true;
    }

    /**
     * Returns a hash code for this instance.
     * 
     * @return A hash code. 
     */
    @Override
    public int hashCode() {
        int hash = 3;
        if (this.label != null) {
            hash = 83 * hash + this.label.hashCode();
        }
        return hash;
    }

    /**
     * Provides serialization support.
     *
     * @param stream  the output stream.
     *
     * @throws IOException  if there is an I/O error.
     */
    private void writeObject(ObjectOutputStream stream) throws IOException {
        stream.defaultWriteObject();
        SerialUtils.writeAttributedString(this.attributedLabel, stream);
        SerialUtils.writePaint(this.labelPaint, stream);
        SerialUtils.writePaint(this.tickLabelPaint, stream);
        SerialUtils.writeStroke(this.axisLineStroke, stream);
        SerialUtils.writePaint(this.axisLinePaint, stream);
        SerialUtils.writeStroke(this.tickMarkStroke, stream);
        SerialUtils.writePaint(this.tickMarkPaint, stream);
    }

    /**
     * Provides serialization support.
     *
     * @param stream  the input stream.
     *
     * @throws IOException  if there is an I/O error.
     * @throws ClassNotFoundException  if there is a classpath problem.
     */
    private void readObject(ObjectInputStream stream)
        throws IOException, ClassNotFoundException {
        stream.defaultReadObject();
        this.attributedLabel = SerialUtils.readAttributedString(stream);
        this.labelPaint = SerialUtils.readPaint(stream);
        this.tickLabelPaint = SerialUtils.readPaint(stream);
        this.axisLineStroke = SerialUtils.readStroke(stream);
        this.axisLinePaint = SerialUtils.readPaint(stream);
        this.tickMarkStroke = SerialUtils.readStroke(stream);
        this.tickMarkPaint = SerialUtils.readPaint(stream);
        this.listenerList = new EventListenerList();
    }

}