001 /* ===========================================================
002 * JFreeChart : a free chart library for the Java(tm) platform
003 * ===========================================================
004 *
005 * (C) Copyright 2000-2007, by Object Refinery Limited and Contributors.
006 *
007 * Project Info: http://www.jfree.org/jfreechart/index.html
008 *
009 * This library is free software; you can redistribute it and/or modify it
010 * under the terms of the GNU Lesser General Public License as published by
011 * the Free Software Foundation; either version 2.1 of the License, or
012 * (at your option) any later version.
013 *
014 * This library is distributed in the hope that it will be useful, but
015 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
016 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
017 * License for more details.
018 *
019 * You should have received a copy of the GNU Lesser General Public
020 * License along with this library; if not, write to the Free Software
021 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
022 * USA.
023 *
024 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
025 * in the United States and other countries.]
026 *
027 * --------------
028 * LogFormat.java
029 * --------------
030 * (C) Copyright 2007, by Object Refinery Limited and Contributors.
031 *
032 * Original Author: David Gilbert (for Object Refinery Limited);
033 * Contributor(s): -;
034 *
035 * Changes
036 * -------
037 * 02-Aug-2007 : Version 1 (DG);
038 *
039 */
040
041 package org.jfree.chart.util;
042
043 import java.text.DecimalFormat;
044 import java.text.FieldPosition;
045 import java.text.NumberFormat;
046 import java.text.ParsePosition;
047
048 /**
049 * A number formatter for logarithmic values. This formatter does not support
050 * parsing.
051 *
052 * @since 1.0.7
053 */
054 public class LogFormat extends NumberFormat {
055
056 /** The log base value. */
057 private double base;
058
059 /** The natural logarithm of the base value. */
060 private double baseLog;
061
062 /** The label for the log base (for example, "e"). */
063 private String baseLabel;
064
065 /** A flag that controls whether or not the base is shown. */
066 private boolean showBase;
067
068 /** The number formatter for the exponent. */
069 private NumberFormat formatter = new DecimalFormat("0.0");
070
071 /**
072 * Creates a new instance.
073 *
074 * @param base the base.
075 * @param baseLabel the base label.
076 * @param showBase a flag that controls whether or not the base value is
077 * shown.
078 */
079 public LogFormat(double base, String baseLabel, boolean showBase) {
080 this.base = base;
081 this.baseLog = Math.log(this.base);
082 this.baseLabel = baseLabel;
083 this.showBase = showBase;
084 }
085
086 /**
087 * Calculates the log of a given value.
088 *
089 * @param value the value.
090 *
091 * @return The log of the value.
092 */
093 private double calculateLog(double value) {
094 return Math.log(value) / this.baseLog;
095 }
096
097 /**
098 * Returns a formatted representation of the specified number.
099 *
100 * @param number the number.
101 * @param toAppendTo the string buffer to append to.
102 * @param pos the position.
103 *
104 * @return A string buffer containing the formatted value.
105 */
106 public StringBuffer format(double number, StringBuffer toAppendTo,
107 FieldPosition pos) {
108 StringBuffer result = new StringBuffer();
109 if (this.showBase) {
110 result.append(this.baseLabel);
111 result.append("^");
112 }
113 result.append(this.formatter.format(calculateLog(number)));
114 return result;
115 }
116
117 /**
118 * Formats the specified number as a hexadecimal string. The decimal
119 * fraction is ignored.
120 *
121 * @param number the number to format.
122 * @param toAppendTo the buffer to append to (ignored here).
123 * @param pos the field position (ignored here).
124 *
125 * @return The string buffer.
126 */
127 public StringBuffer format(long number, StringBuffer toAppendTo,
128 FieldPosition pos) {
129 StringBuffer result = new StringBuffer();
130 if (this.showBase) {
131 result.append(this.baseLabel);
132 result.append("^");
133 }
134 result.append(this.formatter.format(calculateLog(number)));
135 return result;
136 }
137
138 /**
139 * Parsing is not implemented, so this method always returns
140 * <code>null</code>.
141 *
142 * @param source ignored.
143 * @param parsePosition ignored.
144 *
145 * @return Always <code>null</code>.
146 */
147 public Number parse (String source, ParsePosition parsePosition) {
148 return null; // don't bother with parsing
149 }
150
151 }