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Java > Open Source Codes > javax > measure > converters > LogConverter


1 /*
2  * JScience - Java(TM) Tools and Libraries for the Advancement of Sciences.
3  * Copyright (C) 2006 - JScience (http://jscience.org/)
4  * All rights reserved.
5  *
6  * Permission to use, copy, modify, and distribute this software is
7  * freely granted, provided that this notice is preserved.
8  */
9 package javax.measure.converters;
10
11 /**
12  * <p> This class represents a logarithmic converter. Such converter
13  * is typically used to create logarithmic unit. For example:[code]
14  * Unit<Dimensionless> BEL = Unit.ONE.transform(new LogConverter(10).inverse());
15  * [/code]</p>
16  *
17  * <p> Instances of this class are immutable.</p>
18  *
19  * @author <a HREF="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
20  * @version 3.1, April 22, 2006
21  */
22 public final class LogConverter extends UnitConverter {
23
24     /**
25      * Holds the logarithmic base.
26      */
27     private final double _base;
28
29     /**
30      * Holds the natural logarithm of the base.
31      */
32     private final double _logBase;
33
34     /**
35      * Holds the inverse of the natural logarithm of the base.
36      */
37     private final double _invLogBase;
38
39     /**
40      * Holds the inverse of this converter.
41      */
42     private final Inverse _inverse = new Inverse();
43
44     /**
45      * Creates a logarithmic converter having the specified base.
46      *
47      * @param base the logarithmic base (e.g. <code>Math.E</code> for
48      * the Natural Logarithm).
49      */
50     public LogConverter(double base) {
51         _base = base;
52         _logBase = Math.log(base);
53         _invLogBase = 1.0 / _logBase;
54     }
55
56     /**
57      * Returns the logarithmic base of this converter.
58      *
59      * @return the logarithmic base (e.g. <code>Math.E</code> for
60      * the Natural Logarithm).
61      */
62     public double getBase() {
63         return _base;
64     }
65
66     @Override JavaDoc
67     public UnitConverter inverse() {
68         return _inverse;
69     }
70
71     @Override JavaDoc
72     public double convert(double amount) {
73         return _invLogBase * Math.log(amount);
74     }
75
76     @Override JavaDoc
77     public boolean isLinear() {
78         return false;
79     }
80
81     @Override JavaDoc
82     public boolean equals(Object JavaDoc obj) {
83         if (!(obj instanceof LogConverter))
84             return false;
85         LogConverter lc = (LogConverter) obj;
86         return (float) _base == (float) lc._base;
87     }
88
89     @Override JavaDoc
90     public int hashCode() {
91         int h = Float.floatToIntBits((float) _base);
92         h += ~(h << 9);
93         h ^= (h >>> 14);
94         h += (h << 4);
95         return h ^ (h >>> 10);
96     }
97
98     /**
99      * This inner class represents the inverse of the logarithmic converter
100      * (exponentiation converter).
101      */
102     private class Inverse extends UnitConverter {
103
104
105         @Override JavaDoc
106         public UnitConverter inverse() {
107             return LogConverter.this;
108         }
109
110         @Override JavaDoc
111         public double convert(double amount) {
112             return Math.exp(_logBase * amount);
113         }
114
115         @Override JavaDoc
116         public boolean isLinear() {
117             return false;
118         }
119
120         @Override JavaDoc
121         public boolean equals(Object JavaDoc cvtr) {
122             return (cvtr instanceof Inverse)
123             && LogConverter.this.equals(((Inverse) cvtr).inverse());
124         }
125
126         @Override JavaDoc
127         public int hashCode() {
128             return - LogConverter.this.hashCode();
129         }
130
131         private static final long serialVersionUID = 1L;
132     }
133
134     private static final long serialVersionUID = 1L;
135 }
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