001/*
002 * Units of Measurement API
003 * Copyright (c) 2014-2021, Jean-Marie Dautelle, Werner Keil, Otavio Santana.
004 *
005 * All rights reserved.
006 *
007 * Redistribution and use in source and binary forms, with or without modification,
008 * are permitted provided that the following conditions are met:
009 *
010 * 1. Redistributions of source code must retain the above copyright notice,
011 *    this list of conditions and the following disclaimer.
012 *
013 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions
014 *    and the following disclaimer in the documentation and/or other materials provided with the distribution.
015 *
016 * 3. Neither the name of JSR-385 nor the names of its contributors may be used to endorse or promote products
017 *    derived from this software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
020 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
021 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
022 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
023 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
026 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
028 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package javax.measure;
031
032import java.util.List;
033
034/**
035 * A converter of numeric values between different units.
036 *
037 * <p>
038 * Instances of this class are usually obtained through the {@link Unit#getConverterTo(Unit)} method.
039 * </p>
040 *
041 * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
042 * @author <a href="mailto:werner@uom.technology">Werner Keil</a>
043 * @author <a href="mailto:martin.desruisseaux@geomatys.com">Martin
044 *         Desruisseaux</a>
045 * @author <a href="mailto:thodoris.bais@gmail.com">Thodoris Bais</a>
046 * @author <a href="mailto:ahuber@apache.org">Andi Huber</a>
047 * @version 1.4, May 12, 2019
048 * @since 1.0
049 *
050 * @see Unit
051 * @see <a href="http://en.wikipedia.org/wiki/Conversion_of_units"> Wikipedia: Conversion of units</a>
052 */
053public interface UnitConverter {
054
055    /**
056     * Indicates if this converter is an identity converter. The identity converter returns its input argument ({@code convert(x) == x}).
057     * <p>
058     * Note: Identity converters are also always 'linear', see {@link UnitConverter#isLinear()}.
059     * </p>
060     *
061     * @return {@code true} if this converter is an identity converter.
062     */
063    boolean isIdentity();
064
065    /**
066     * Indicates whether this converter represents a (one-dimensional) linear transformation, that is
067     * a <a href="https://en.wikipedia.org/wiki/Linear_map">linear map (wikipedia)</a> from a one-dimensional 
068     * vector space (a scalar) to a one-dimensional vector space. Typically from 'R' to 'R', with 'R' the 
069     * real numbers.  
070     *
071     * <p>
072     * Given such a 'linear' converter 'A', let 'u', 'v' and 'r' be arbitrary numbers, then the following 
073     * must hold by definition: 
074     *
075     * <ul>
076     * <li>{@code A(u + v) == A(u) + A(v)}</li>
077     * <li>{@code A(r * u) == r * A(u)}</li>
078     * </ul>
079     *
080     * <p>
081     * Given a second 'linear' converter 'B', commutativity of composition follows by above definition:
082     *
083     * <ul>
084     * <li>{@code (A o B) (u) == (B o A) (u)}</li>
085     * </ul>
086     * 
087     * In other words, two 'linear' converters do have the property that {@code A(B(u)) == B(A(u))}, meaning 
088     * for 'A' and 'B' the order of their composition does not matter. Expressed as Java code:
089     *
090     * <p>
091     *{@code A.concatenate(B).convert(u) == B.concatenate(A).convert(u)}
092     * </p>
093     * 
094     * Note: For composing UnitConverters see also {@link UnitConverter#concatenate(UnitConverter)}.
095     *
096     * @return {@code true} if this converter represents a linear transformation; 
097     * {@code false} otherwise.
098     * 
099     */
100    boolean isLinear();
101
102    /**
103     * Returns the inverse of this converter. If {@code x} is a valid value, then {@code x == inverse().convert(convert(x))} to within the accuracy of
104     * computer arithmetic.
105     *
106     * @return the inverse of this converter.
107     */
108    UnitConverter inverse();
109
110    /**
111     * Converts a {@code Number} value.
112     *
113     * @param value
114     *          the {@code Number} value to convert.
115     * @return the {@code Number} value after conversion.
116     */
117    Number convert(Number value);
118
119    /**
120     * Converts a {@code double} value.
121     *
122     * @param value
123     *          the numeric value to convert.
124     * @return the {@code double} value after conversion.
125     */
126    double convert(double value);
127
128    /**
129     * Concatenates this converter with another converter. The resulting converter is equivalent to first converting by the specified converter (right
130     * converter), and then converting by this converter (left converter).
131     *
132     * @param converter
133     *          the other converter to concatenate with this converter.
134     * @return the concatenation of this converter with the other converter.
135     */
136    UnitConverter concatenate(UnitConverter converter);
137
138    /**
139     * <p>
140     * Returns the steps of fundamental converters making up this converter or {@code this} if the converter is a fundamental converter.
141     * </p>
142     * <p>
143     * For example, {@code converter1.getConversionSteps()} returns {@code converter1} while
144     * {@code converter1.concatenate(converter2).getConversionSteps()} returns {@code converter1, converter2}.
145     * </p>
146     *
147     * @return the list of fundamental converters which concatenated make up this converter.
148     */
149    List<? extends UnitConverter> getConversionSteps();
150}