| /* |
| * JScience - Java(TM) Tools and Libraries for the Advancement of Sciences. |
| * Copyright (C) 2006 - JScience (http://jscience.org/) |
| * All rights reserved. |
| * |
| * Permission to use, copy, modify, and distribute this software is |
| * freely granted, provided that this notice is preserved. |
| */ |
| package javax.measure.unit; |
| |
| import javax.measure.converter.UnitConverter; |
| import javax.measure.quantity.Quantity; |
| |
| /** |
| * <p> This class represents the units used in expressions to distinguish |
| * between quantities of a different nature but of the same dimensions.</p> |
| * |
| * <p> Instances of this class are created through the |
| * {@link Unit#alternate(String)} method.</p> |
| * |
| * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a> |
| * @version 4.2, August 26, 2007 |
| */ |
| public final class AlternateUnit<Q extends Quantity> extends DerivedUnit<Q> { |
| |
| /** |
| * Holds the symbol. |
| */ |
| private final String _symbol; |
| |
| /** |
| * Holds the parent unit (a system unit). |
| */ |
| private final Unit<?> _parent; |
| |
| /** |
| * Creates an alternate unit for the specified unit identified by the |
| * specified symbol. |
| * |
| * @param symbol the symbol for this alternate unit. |
| * @param parent the system unit from which this alternate unit is |
| * derived. |
| * @throws UnsupportedOperationException if the source is not |
| * a standard unit. |
| * @throws IllegalArgumentException if the specified symbol is |
| * associated to a different unit. |
| */ |
| AlternateUnit(String symbol, Unit<?> parent) { |
| if (!parent.isStandardUnit()) |
| throw new UnsupportedOperationException(this |
| + " is not a standard unit"); |
| _symbol = symbol; |
| _parent = parent; |
| // Checks if the symbol is associated to a different unit. |
| synchronized (Unit.SYMBOL_TO_UNIT) { |
| Unit<?> unit = Unit.SYMBOL_TO_UNIT.get(symbol); |
| if (unit == null) { |
| Unit.SYMBOL_TO_UNIT.put(symbol, this); |
| return; |
| } |
| if (unit instanceof AlternateUnit) { |
| AlternateUnit<?> existingUnit = (AlternateUnit<?>) unit; |
| if (symbol.equals(existingUnit._symbol) |
| && _parent.equals(existingUnit._parent)) |
| return; // OK, same unit. |
| } |
| throw new IllegalArgumentException("Symbol " + symbol |
| + " is associated to a different unit"); |
| } |
| } |
| |
| /** |
| * Returns the symbol for this alternate unit. |
| * |
| * @return this alternate unit symbol. |
| */ |
| public final String getSymbol() { |
| return _symbol; |
| } |
| |
| /** |
| * Returns the parent unit from which this alternate unit is derived |
| * (a system unit itself). |
| * |
| * @return the parent of the alternate unit. |
| */ |
| @SuppressWarnings("unchecked") |
| public final Unit<? super Q> getParent() { |
| return (Unit<? super Q>) _parent; |
| } |
| |
| @Override |
| public final Unit<? super Q> getStandardUnit() { |
| return this; |
| } |
| |
| @Override |
| public final UnitConverter toStandardUnit() { |
| return UnitConverter.IDENTITY; |
| } |
| |
| /** |
| * Indicates if this alternate unit is considered equals to the specified |
| * object (both are alternate units with equal symbol, equal base units |
| * and equal converter to base units). |
| * |
| * @param that the object to compare for equality. |
| * @return <code>true</code> if <code>this</code> and <code>that</code> |
| * are considered equals; <code>false</code>otherwise. |
| */ |
| public boolean equals(Object that) { |
| if (this == that) |
| return true; |
| if (!(that instanceof AlternateUnit)) |
| return false; |
| AlternateUnit<?> thatUnit = (AlternateUnit<?>) that; |
| return this._symbol.equals(thatUnit._symbol); // Symbols are unique. |
| } |
| |
| // Implements abstract method. |
| public int hashCode() { |
| return _symbol.hashCode(); |
| } |
| |
| private static final long serialVersionUID = 1L; |
| } |