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The ucar.units Java package is for decoding and encoding formatted unit specifications (e.g. "m/s"), converting numeric values between compatible units (e.g. between "m/s" and "knot"), and for performing arithmetic operations on units (e.g. dividing one unit by another, or raising a unit to a power).

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/*
 * Copyright (c) 1998-2018 University Corporation for Atmospheric Research/Unidata
 * See LICENSE for license information.
 */
package ucar.units;

import java.io.Serializable;
import java.util.HashMap;
import java.util.Iterator;

/**
 * @author Steven R. Emmerson
 */
public class UnitSystemImpl implements UnitSystem, Serializable {
	private static final long						serialVersionUID	= 1L;

	/**
	 * The quantity-to-base-unit map.
	 * 
	 * @serial
	 */
	private final HashMap	quantityMap;

	/**
	 * The base unit database;
	 * 
	 * @serial
	 */
	private final UnitDB							baseUnitDB;

	/**
	 * The complete database;
	 * 
	 * @serial
	 */
	private final UnitDBImpl						acceptableUnitDB;

	/**
	 * Constructs from a base unit database and a derived unit database.
	 * 
	 * @param baseUnitDB
	 *            The base unit database. Shall only contain base units.
	 * @param derivedUnitDB
	 *            The derived unit database. Shall not contain any base units.
	 * @throws UnitExistsException
	 *             A unit with the same identifier exists in both databases.
	 */
	protected UnitSystemImpl(final UnitDBImpl baseUnitDB,
			final UnitDBImpl derivedUnitDB) throws UnitExistsException {
		quantityMap = new HashMap(baseUnitDB
				.nameCount());
		for (final Iterator iter = baseUnitDB.getIterator(); iter.hasNext();) {
			final Unit unit = (Unit) iter.next();
			final BaseUnit baseUnit = (BaseUnit) unit;
			quantityMap.put(baseUnit.getBaseQuantity(), baseUnit);
		}
		this.baseUnitDB = baseUnitDB;
		acceptableUnitDB = new UnitDBImpl(baseUnitDB.nameCount()
				+ derivedUnitDB.nameCount(), baseUnitDB.symbolCount()
				+ derivedUnitDB.symbolCount());
		acceptableUnitDB.add(baseUnitDB);
		acceptableUnitDB.add(derivedUnitDB);
	}

	/**
	 * Returns the base unit database.
	 * 
	 * @return The base unit database.
	 */
	public final UnitDB getBaseUnitDB() {
		return baseUnitDB;
	}

	/**
	 * Returns the complete unit database.
	 * 
	 * @return The complete unit database (both base units and derived units).
	 */
	public final UnitDB getUnitDB() {
		return acceptableUnitDB;
	}

	/**
	 * Returns the base unit corresponding to a base quantity.
	 * 
	 * @param quantity
	 *            The base quantity.
	 * @return The base unit corresponding to the base quantity in this system
	 *         of units or 
     *				null if no such unit exists.
	 */
	public final BaseUnit getBaseUnit(final BaseQuantity quantity) {
		return quantityMap.get(quantity);
	}
}