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Unit Standard (JSR 363) Reference Implementation.
There is a newer version: 1.0.3
/**
 *  Unit-API - Units of Measurement API for Java
 *  Copyright (c) 2005-2014, Jean-Marie Dautelle, Werner Keil, V2COM.
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
 *
 * 3. Neither the name of JSR-363 nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package tec.units.ri.function;

import static tec.units.ri.function.MathHelper.*;

import javax.measure.UnitConverter;

import tec.units.ri.AbstractConverter;

/**
 *  This class represents a converter multiplying numeric values by an
 *     exact scaling factor (represented as the quotient of two
 *     BigInteger numbers).
 *
 * @author  Jean-Marie Dautelle
 * @author Werner Keil
 * @version 0.5.2, December 24, 2014
 */
public final class RationalConverter extends AbstractConverter 
	implements ValueSupplier {

    /**
	 * 
	 */
//	private static final long serialVersionUID = 1L;

	/**
     * Holds the converter dividend.
     */
    private final double dividend;

    /**
     * Holds the converter divisor (always positive).
     */
    private final double divisor;

    /**
     * Constructor
     *
     * @param dividend the dividend.
     * @param divisor the positive divisor.
     * @throws IllegalArgumentException if divisor <= 0
     * @throws IllegalArgumentException if dividend == divisor
     */
    public RationalConverter (double dividend, double divisor) {
    	this.dividend = dividend;
    	this.divisor = divisor;
    }

    /**
     * Convenience method equivalent to
     * new RationalConverter(dividend, divisor)
     *
     * @param dividend the dividend.
     * @param divisor the positive divisor.
     * @throws IllegalArgumentException if divisor <= 0
     * @throws IllegalArgumentException if dividend == divisor
     */
    public static final RationalConverter of(long dividend, long divisor) {
    	return new RationalConverter((double)dividend, (double)divisor);
    }
    
    /**
     * Convenience method equivalent to
     * new RationalConverter(dividend, divisor)
     *
     * @param dividend the dividend.
     * @param divisor the positive divisor.
     * @throws IllegalArgumentException if divisor <= 0
     * @throws IllegalArgumentException if dividend == divisor
     */
    public static final RationalConverter of(double dividend, double divisor) {
    	return new RationalConverter(dividend, divisor);
    }
    
    /**
     * Returns the integer dividend for this rational converter.
     *
     * @return this converter dividend.
     */
    public double getDividend() {
        return dividend;
    }

    /**
     * Returns the integer (positive) divisor for this rational converter.
     *
     * @return this converter divisor.
     */
    public double getDivisor() {
        return divisor;
    }

    @Override
    public double convert(double value) {
        return value * ((double) dividend / (double)divisor);
    }

    @Override
    public UnitConverter concatenate(UnitConverter converter) {
        if (!(converter instanceof RationalConverter))
            return super.concatenate(converter);
        RationalConverter that = (RationalConverter) converter;
        double newDividend = this.getDividend() * that.getDividend();
        double newDivisor = this.getDivisor() * that.getDivisor();
        double gcd = gcd(newDividend,newDivisor);
        newDividend = newDividend / gcd; // TODO clarify if this works with long
        newDivisor = newDivisor / gcd;
        return (newDividend == 1 && newDivisor == 1)
                ? IDENTITY : new RationalConverter(newDividend, newDivisor);
    }

    @Override
    public RationalConverter inverse() {
        return Math.signum(dividend) == -1 ? new RationalConverter(negateExact(getDivisor()), negateExact(getDividend()))
                : new RationalConverter(getDivisor(), getDividend());
    }

    @Override
    public final String toString() {
        return "RationalConverter(" + dividend + "," + divisor + ")";
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof RationalConverter))
            return false;
        RationalConverter that = (RationalConverter) obj;
        return (this.dividend == that.dividend
                && this.divisor == that.divisor);
    }

    @Override
    public int hashCode() {
        return Double.valueOf(dividend).hashCode() + Double.valueOf(dividend).hashCode();
    }

    @Override
    public boolean isLinear() {
        return true;
    }
    
    public double getAsDouble() {
    	return (double)dividend / (double) divisor;
    }
    
    @Override
	public Double getValue() {
		return Double.valueOf(getAsDouble());
	}
}