| 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.converter; |
| 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 |
| 67 | public UnitConverter inverse() { |
| 68 | return _inverse; |
| 69 | } |
| 70 | |
| 71 | @Override |
| 72 | public double convert(double amount) { |
| 73 | return _invLogBase * Math.log(amount); |
| 74 | } |
| 75 | |
| 76 | @Override |
| 77 | public boolean isLinear() { |
| 78 | return false; |
| 79 | } |
| 80 | |
| 81 | /** |
| 82 | * This inner class represents the inverse of the logarithmic converter |
| 83 | * (exponentiation converter). |
| 84 | */ |
| 85 | private class Inverse extends UnitConverter { |
| 86 | |
| 87 | |
| 88 | @Override |
| 89 | public UnitConverter inverse() { |
| 90 | return LogConverter.this; |
| 91 | } |
| 92 | |
| 93 | @Override |
| 94 | public double convert(double amount) { |
| 95 | return Math.exp(_logBase * amount); |
| 96 | } |
| 97 | |
| 98 | @Override |
| 99 | public boolean isLinear() { |
| 100 | return false; |
| 101 | } |
| 102 | |
| 103 | private static final long serialVersionUID = 1L; |
| 104 | } |
| 105 | |
| 106 | private static final long serialVersionUID = 1L; |
| 107 | } |