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Unit Standard (JSR 363) Reference Implementation.
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/**
 *  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;

import javax.measure.Quantity;
import javax.measure.Unit;
import javax.measure.quantity.Dimensionless;

import tec.units.ri.function.UnitSupplier;
import tec.units.ri.function.ValueSupplier;
import tec.units.ri.quantity.NumberQuantity;
import tec.units.ri.unit.Units;

/**
 * 
 * This class represents the immutable result of a scalar measurement stated in
 * a known unit.
 * 
 * 
 * 
 * 
 *         public static final Quantity C = AbstractQuantity.of("299792458 m/s").asType(Velocity.class);
 *         // Speed of Light (exact).
 *    
 * 
 * 
 * 
 * Quantities can be converted to different units.

 * 
 *         Quantity milesPerHour = C.to(MILES_PER_HOUR); // Use double implementation (fast).
 *         System.out.println(milesPerHour);
 * 
 *         > 670616629.3843951 m/h
 *     
 * 
 * 
 * 
 * Applications may sub-class {@link AbstractQuantity} for particular quantity
 * types.

 * 
 *         // Quantity of type Mass based on double primitive
 * types.

 * public class MassAmount extends AbstractQuantity {

 * private final double kilograms; // Internal SI representation.

 * private Mass(double kg) { kilograms = kg; }

 * public static Mass of(double value, Unit unit) {

 * return new Mass(unit.getConverterTo(SI.KILOGRAM).convert(value));

 * }

 * public Unit getUnit() { return SI.KILOGRAM; }

 * public Double getValue() { return _kilograms; }

 * ...

 * }

 * 

 * 
 * // Complex numbers measurements.

 * public class ComplexQuantity
 * extends AbstractQuantity
 * {

 * public Complex getValue() { ... } // Assuming Complex is a Number.

 * ...

 * }

 * 

 * // Specializations of complex numbers measurements.

 * public final class Current extends ComplexQuantity {...}

 * public final class Tension extends ComplexQuantity {...}

 * 
 * 
 * 
 * 
 * All instances of this class shall be immutable.
 * 
 * 
 * @author Werner Keil
 * @version 0.6.3, $Date: 2015-04-19 $
 */
public abstract class AbstractQuantity> implements
		Quantity, Comparable>, UnitSupplier, ValueSupplier {

	/**
	 * 
	 */
	// private static final long serialVersionUID = -4993173119977931016L;

	private final Unit unit;

	/**
	 * Holds a dimensionless quantity of none (exact).
	 */
	public static final AbstractQuantity NONE = NumberQuantity.of(0, Units.ONE);

	/**
	 * Holds a dimensionless quantity of one (exact).
	 */
	public static final AbstractQuantity ONE = NumberQuantity.of(1, Units.ONE);

	/**
	 * constructor.
	 */
	protected AbstractQuantity(Unit unit) {
		this.unit = unit;
	}

	/**
	 * Returns the measurement numeric value.
	 *
	 * @return the measurement value.
	 */
	public abstract Number getValue();

	/**
	 * Returns the measurement unit.
	 *
	 * @return the measurement unit.
	 */
	public Unit getUnit() {
		return unit;
	}

	/**
	 * Convenient method equivalent to {@link #to(javax.measure.unit.Unit)
	 * to(this.getUnit().toSI())}.
	 *
	 * @return this measure or a new measure equivalent to this measure but
	 *         stated in SI units.
	 * @throws ArithmeticException
	 *             if the result is inexact and the quotient has a
	 *             non-terminating decimal expansion.
	 */
	public AbstractQuantity toSI() {
		return to(this.getUnit().getSystemUnit());
	}

	/**
	 * Returns this measure after conversion to specified unit. The default
	 * implementation returns
	 * Measure.valueOf(doubleValue(unit), unit). If this measure is
	 * already stated in the specified unit, then this measure is returned and
	 * no conversion is performed.
	 *
	 * @param unit
	 *            the unit in which the returned measure is stated.
	 * @return this measure or a new measure equivalent to this measure but
	 *         stated in the specified unit.
	 * @throws ArithmeticException
	 *             if the result is inexact and the quotient has a
	 *             non-terminating decimal expansion.
	 */
	public AbstractQuantity to(Unit unit) {
		if (unit.equals(this.getUnit())) {
			return this;
		}
		return NumberQuantity.of(doubleValue(unit), unit);
	}

	/**
	 * Compares this measure to the specified Measurement quantity. The default
	 * implementation compares the {@link AbstractQuantity#doubleValue(Unit)} of both
	 * this measure and the specified Measurement stated in the same unit (this
	 * measure's {@link #getUnit() unit}).
	 *
	 * @return a negative integer, zero, or a positive integer as this measure
	 *         is less than, equal to, or greater than the specified Measurement
	 *         quantity.
	 * @return Double.compare(this.doubleValue(getUnit()),
	 *         that.doubleValue(getUnit()))
	 */
	public int compareTo(Quantity that) {
		Unit unit = getUnit();
		return Double.compare(doubleValue(unit), that.getValue().doubleValue());
	}

	/**
	 * Compares this measure against the specified object for strict
	 * equality (same unit and same amount).
	 *
	 * 
	 * Similarly to the {@link BigDecimal#equals} method which consider 2.0 and
	 * 2.00 as different objects because of different internal scales,
	 * measurements such as Measure.valueOf(3.0, KILOGRAM)
	 * Measure.valueOf(3, KILOGRAM) and
	 * Quantities.getQuantity("3 kg") might not be considered equals
	 * because of possible differences in their implementations.
	 * 
	 *
	 * 
	 * To compare measures stated using different units or using different
	 * amount implementations the {@link #compareTo compareTo} or
	 * {@link #equals(javax.measure.Measurement, double, javax.measure.unit.Unit)
	 * equals(Measurement, epsilon, epsilonUnit)} methods should be used.
	 * 
	 *
	 * @param obj
	 *            the object to compare with.
	 * @return this.getUnit.equals(obj.getUnit())
	 *         && this.getValue().equals(obj.getValue())
	 */
	@Override
	public boolean equals(Object obj) {
		if (!(obj instanceof AbstractQuantity)) {
			return false;
		}
		AbstractQuantity that = (AbstractQuantity) obj;
		return this.getUnit().equals(that.getUnit())
				&& this.getValue().equals(that.getValue());
	}

	/**
	 * Compares this measure and the specified Measurement to the given
	 * accuracy. Measurements are considered approximately equals if their
	 * absolute differences when stated in the same specified unit is less than
	 * the specified epsilon.
	 *
	 * @param that
	 *            the Measurement to compare with.
	 * @param epsilon
	 *            the absolute error stated in epsilonUnit.
	 * @param epsilonUnit
	 *            the epsilon unit.
	 * @return abs(this.doubleValue(epsilonUnit) - that.doubleValue(epsilonUnit)) <= epsilon
	 */
	public boolean equals(AbstractQuantity that, double epsilon,
			Unit epsilonUnit) {
		return Math.abs(this.doubleValue(epsilonUnit)
				- that.doubleValue(epsilonUnit)) <= epsilon;
	}

	/**
	 * Returns the hash code for this measure.
	 *
	 * @return the hash code value.
	 */
	@Override
	public int hashCode() {
		return getUnit().hashCode() + getValue().hashCode();
	}

	final boolean isBig() {
		return false;
	}

	/**
	 * Returns the String representation of this measure. The
	 * string produced for a given measure is always the same; it is not
	 * affected by locale. This means that it can be used as a canonical string
	 * representation for exchanging measure, or as a key for a Hashtable, etc.
	 * Locale-sensitive measure formatting and parsing is handled by the
	 * {@link MeasurementFormat} class and its subclasses.
	 *
	 * @return UnitFormat.getInternational().format(this)
	 */
	@Override
	public String toString() {
		// return MeasureFormat.getStandard().format(this); TODO improve
		// MeasureFormat
		return String.valueOf(getValue()) + " " + String.valueOf(getUnit());
	}

	public abstract double doubleValue(Unit unit) throws ArithmeticException;

	protected long longValue(Unit unit) throws ArithmeticException {
		double result = doubleValue(unit);
		if ((result < Long.MIN_VALUE) || (result > Long.MAX_VALUE)) {
			throw new ArithmeticException("Overflow (" + result + ")");
		}
		return (long) result;
	}

	protected float floatValue(Unit unit) {
		return (float) doubleValue(unit);
	}

	/**
	 * Casts this quantity to a parameterized unit of specified nature or throw a
	 * ClassCastException if the dimension of the specified
	 * quantity and this measure unit's dimension do not match. For example:

	 * 
	 *     Measure length = Quantities.getQuantity("2 km").asType(Length.class);
	 * 
	 *
	 * @param type
	 *            the quantity class identifying the nature of the quantity.
	 * @return this quantity parameterized with the specified type.
	 * @throws ClassCastException
	 *             if the dimension of this unit is different from the specified
	 *             quantity dimension.
	 * @throws UnsupportedOperationException
	 *             if the specified quantity class does not have a public static
	 *             field named "UNIT" holding the SI unit for the quantity.
	 * @see Unit#asType(Class)
	 */
	@SuppressWarnings("unchecked")
	public final > AbstractQuantity asType(
			Class type) throws ClassCastException {
		this.getUnit().asType(type); // Raises ClassCastException is dimension mismatches.
		return (AbstractQuantity) this;
	}
}