Source for org.jfree.chart.util.LogFormat

   1: /* ===========================================================
   2:  * JFreeChart : a free chart library for the Java(tm) platform
   3:  * ===========================================================
   4:  *
   5:  * (C) Copyright 2000-2007, by Object Refinery Limited and Contributors.
   6:  *
   7:  * Project Info:  http://www.jfree.org/jfreechart/index.html
   8:  *
   9:  * This library is free software; you can redistribute it and/or modify it
  10:  * under the terms of the GNU Lesser General Public License as published by
  11:  * the Free Software Foundation; either version 2.1 of the License, or
  12:  * (at your option) any later version.
  13:  *
  14:  * This library is distributed in the hope that it will be useful, but
  15:  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  16:  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
  17:  * License for more details.
  18:  *
  19:  * You should have received a copy of the GNU Lesser General Public
  20:  * License along with this library; if not, write to the Free Software
  21:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
  22:  * USA.  
  23:  *
  24:  * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
  25:  * in the United States and other countries.]
  26:  *
  27:  * --------------
  28:  * LogFormat.java
  29:  * --------------
  30:  * (C) Copyright 2007, by Object Refinery Limited and Contributors.
  31:  *
  32:  * Original Author:  David Gilbert (for Object Refinery Limited);
  33:  * Contributor(s):   -;
  34:  *
  35:  * Changes
  36:  * -------
  37:  * 02-Aug-2007 : Version 1 (DG);
  38:  * 
  39:  */
  40: 
  41: package org.jfree.chart.util;
  42: 
  43: import java.text.DecimalFormat;
  44: import java.text.FieldPosition;
  45: import java.text.NumberFormat;
  46: import java.text.ParsePosition;
  47: 
  48: /**
  49:  * A number formatter for logarithmic values.  This formatter does not support
  50:  * parsing.
  51:  * 
  52:  * @since 1.0.7
  53:  */
  54: public class LogFormat extends NumberFormat {
  55:     
  56:     /** The log base value. */
  57:     private double base;
  58:     
  59:     /** The natural logarithm of the base value. */
  60:     private double baseLog;
  61:     
  62:     /** The label for the log base (for example, "e"). */
  63:     private String baseLabel;
  64:     
  65:     /** A flag that controls whether or not the base is shown. */
  66:     private boolean showBase;
  67:     
  68:     /** The number formatter for the exponent. */
  69:     private NumberFormat formatter = new DecimalFormat("0.0");
  70:     
  71:     /**
  72:      * Creates a new instance.
  73:      * 
  74:      * @param base  the base.
  75:      * @param baseLabel  the base label.
  76:      * @param showBase  a flag that controls whether or not the base value is
  77:      *                  shown.
  78:      */
  79:     public LogFormat(double base, String baseLabel, boolean showBase) {
  80:         this.base = base;
  81:         this.baseLog = Math.log(this.base);
  82:         this.baseLabel = baseLabel;
  83:         this.showBase = showBase;
  84:     }
  85:     
  86:     /**
  87:      * Calculates the log of a given value.
  88:      * 
  89:      * @param value  the value.
  90:      * 
  91:      * @return The log of the value.
  92:      */
  93:     private double calculateLog(double value) {
  94:         return Math.log(value) / this.baseLog;
  95:     }
  96:     
  97:     /**
  98:      * Returns a formatted representation of the specified number.
  99:      * 
 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: }