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JFreeChart is a class library, written in Java, for generating charts. Utilising the Java2D APIs, it currently supports bar charts, pie charts, line charts, XY-plots and time series plots.

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/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2005, 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.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------------------------
 * StandardTickUnitSource.java
 * ---------------------------
 * (C) Copyright 2003, 2004, by Object Refinery Limited.
 *
 * Original Author:  David Gilbert (for Object Refinery Limited);
 * Contributor(s):   -;
 *
 * $Id: StandardTickUnitSource.java,v 1.2.2.2 2006/01/27 13:53:28 mungady Exp $
 *
 * Changes
 * -------
 * 23-Sep-2003 : Version 1 (DG);
 *
 */

package org.jfree.chart.axis;

import java.text.DecimalFormat;

/**
 * A source that can used by the {@link NumberAxis} class to obtain a
 * suitable {@link TickUnit}.
 */
public class StandardTickUnitSource implements TickUnitSource {

    /** Constant for log(10.0). */
    private static final double LOG_10_VALUE = Math.log(10.0);
    
    /**
     * Returns a tick unit that is larger than the supplied unit.
     *
     * @param unit  the unit (null not permitted).
     *
     * @return A tick unit that is larger than the supplied unit.
     */
    public TickUnit getLargerTickUnit(TickUnit unit) {
        double x = unit.getSize();
        double log = Math.log(x) / LOG_10_VALUE;
        double higher = Math.ceil(log);
        return new NumberTickUnit(Math.pow(10, higher), 
                new DecimalFormat("0.0E0"));
    }

    /**
     * Returns the tick unit in the collection that is greater than or equal
     * to (in size) the specified unit.
     *
     * @param unit  the unit (null not permitted).
     *
     * @return A unit from the collection.
     */
    public TickUnit getCeilingTickUnit(TickUnit unit) {
        return getLargerTickUnit(unit);
    }

    /**
     * Returns the tick unit in the collection that is greater than or equal
     * to the specified size.
     *
     * @param size  the size.
     *
     * @return A unit from the collection.
     */
    public TickUnit getCeilingTickUnit(double size) {
        double log = Math.log(size) / LOG_10_VALUE;
        double higher = Math.ceil(log);
        return new NumberTickUnit(Math.pow(10, higher), 
                new DecimalFormat("0.0E0"));
    }
    
}