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JFreeChart is a class library, written in Java, for generating charts. Utilising the Java2D API, it supports a wide range of chart types including bar charts, pie charts, line charts, XY-plots, time series plots, Sankey charts and more.
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/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2011, 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.]
 *
 * ----------------
 * ArrowNeedle.java
 * ----------------
 * (C) Copyright 2002-2008, by the Australian Antarctic Division and
 *                          Contributors.
 *
 * Original Author:  Bryan Scott (for the Australian Antarctic Division);
 * Contributor(s):   David Gilbert (for Object Refinery Limited);
 *
 * Changes:
 * --------
 * 25-Sep-2002 : Version 1, contributed by Bryan Scott (DG);
 * 27-Mar-2003 : Implemented Serializable (DG);
 * 09-Sep-2003 : Added equals() method (DG);
 * 08-Jun-2005 : Implemented Cloneable (DG);
 * 22-Nov-2007 : Added hashCode() implementation (DG);
 *
 */

package org.jfree.chart.needle;

import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.geom.GeneralPath;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import java.io.Serializable;

import org.jfree.chart.HashUtilities;

/**
 * A needle in the shape of an arrow.
 */
public class ArrowNeedle extends MeterNeedle
                         implements Cloneable, Serializable {

    /** For serialization. */
    private static final long serialVersionUID = -5334056511213782357L;

    /**
     * A flag controlling whether or not there is an arrow at the top of the
     * needle.
     */
    private boolean isArrowAtTop = true;

    /**
     * Constructs a new arrow needle.
     *
     * @param isArrowAtTop  a flag that controls whether or not there is an
     *                      arrow at the top of the needle.
     */
    public ArrowNeedle(boolean isArrowAtTop) {
        this.isArrowAtTop = isArrowAtTop;
    }

    /**
     * Draws the needle.
     *
     * @param g2  the graphics device.
     * @param plotArea  the plot area.
     * @param rotate  the rotation point.
     * @param angle  the angle.
     */
    protected void drawNeedle(Graphics2D g2, Rectangle2D plotArea,
                              Point2D rotate, double angle) {

        Line2D shape = new Line2D.Float();
        Shape d = null;

        float x = (float) (plotArea.getMinX() +  (plotArea.getWidth() / 2));
        float minY = (float) plotArea.getMinY();
        float maxY = (float) plotArea.getMaxY();
        shape.setLine(x, minY, x, maxY);

        GeneralPath shape1 = new GeneralPath();
        if (this.isArrowAtTop) {
            shape1.moveTo(x, minY);
            minY += 4 * getSize();
        }
        else {
            shape1.moveTo(x, maxY);
            minY = maxY - 4 * getSize();
        }
        shape1.lineTo(x + getSize(), minY);
        shape1.lineTo(x - getSize(), minY);
        shape1.closePath();

        if ((rotate != null) && (angle != 0)) {
            getTransform().setToRotation(angle, rotate.getX(), rotate.getY());
            d = getTransform().createTransformedShape(shape);
        }
        else {
            d = shape;
        }
        defaultDisplay(g2, d);

        if ((rotate != null) && (angle != 0)) {
            d = getTransform().createTransformedShape(shape1);
        }
        else {
            d = shape1;
        }
        defaultDisplay(g2, d);

    }

    /**
     * Tests another object for equality with this object.
     *
     * @param obj  the object to test (null permitted).
     *
     * @return A boolean.
     */
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof ArrowNeedle)) {
            return false;
        }
        if (!super.equals(obj)) {
            return false;
        }
        ArrowNeedle that = (ArrowNeedle) obj;
        if (this.isArrowAtTop != that.isArrowAtTop) {
            return false;
        }
        return true;
    }

    /**
     * Returns a hash code for this instance.
     *
     * @return A hash code.
     */
    public int hashCode() {
        int result = super.hashCode();
        result = HashUtilities.hashCode(result, this.isArrowAtTop);
        return result;
    }

    /**
     * Returns a clone of this needle.
     *
     * @return A clone.
     *
     * @throws CloneNotSupportedException if the ArrowNeedle
     *     cannot be cloned (in theory, this should not happen).
     */
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

}