| 1 | /* |
| 2 | * JScience - Java(TM) Tools and Libraries for the Advancement of Sciences. |
| 3 | * Copyright (C) 2006 - JScience (http://jscience.org/) |
| 4 | * All rights reserved. |
| 5 | * |
| 6 | * Permission to use, copy, modify, and distribute this software is |
| 7 | * freely granted, provided that this notice is preserved. |
| 8 | */ |
| 9 | package javax.measure.unit; |
| 10 | |
| 11 | import javax.measure.converter.UnitConverter; |
| 12 | import javax.measure.quantity.Quantity; |
| 13 | |
| 14 | /** |
| 15 | * <p> This class represents the units used in expressions to distinguish |
| 16 | * between quantities of a different nature but of the same dimensions.</p> |
| 17 | * |
| 18 | * <p> Instances of this class are created through the |
| 19 | * {@link Unit#alternate(String)} method.</p> |
| 20 | * |
| 21 | * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a> |
| 22 | * @version 4.2, August 26, 2007 |
| 23 | */ |
| 24 | public final class AlternateUnit<Q extends Quantity> extends DerivedUnit<Q> { |
| 25 | |
| 26 | /** |
| 27 | * Holds the symbol. |
| 28 | */ |
| 29 | private final String _symbol; |
| 30 | |
| 31 | /** |
| 32 | * Holds the parent unit (a system unit). |
| 33 | */ |
| 34 | private final Unit<?> _parent; |
| 35 | |
| 36 | /** |
| 37 | * Creates an alternate unit for the specified unit identified by the |
| 38 | * specified symbol. |
| 39 | * |
| 40 | * @param symbol the symbol for this alternate unit. |
| 41 | * @param parent the system unit from which this alternate unit is |
| 42 | * derived. |
| 43 | * @throws UnsupportedOperationException if the source is not |
| 44 | * a standard unit. |
| 45 | * @throws IllegalArgumentException if the specified symbol is |
| 46 | * associated to a different unit. |
| 47 | */ |
| 48 | AlternateUnit(String symbol, Unit<?> parent) { |
| 49 | if (!parent.isStandardUnit()) |
| 50 | throw new UnsupportedOperationException(this |
| 51 | + " is not a standard unit"); |
| 52 | _symbol = symbol; |
| 53 | _parent = parent; |
| 54 | // Checks if the symbol is associated to a different unit. |
| 55 | synchronized (Unit.SYMBOL_TO_UNIT) { |
| 56 | Unit<?> unit = Unit.SYMBOL_TO_UNIT.get(symbol); |
| 57 | if (unit == null) { |
| 58 | Unit.SYMBOL_TO_UNIT.put(symbol, this); |
| 59 | return; |
| 60 | } |
| 61 | if (unit instanceof AlternateUnit) { |
| 62 | AlternateUnit<?> existingUnit = (AlternateUnit<?>) unit; |
| 63 | if (symbol.equals(existingUnit._symbol) |
| 64 | && _parent.equals(existingUnit._parent)) |
| 65 | return; // OK, same unit. |
| 66 | } |
| 67 | throw new IllegalArgumentException("Symbol " + symbol |
| 68 | + " is associated to a different unit"); |
| 69 | } |
| 70 | } |
| 71 | |
| 72 | /** |
| 73 | * Returns the symbol for this alternate unit. |
| 74 | * |
| 75 | * @return this alternate unit symbol. |
| 76 | */ |
| 77 | public final String getSymbol() { |
| 78 | return _symbol; |
| 79 | } |
| 80 | |
| 81 | /** |
| 82 | * Returns the parent unit from which this alternate unit is derived |
| 83 | * (a system unit itself). |
| 84 | * |
| 85 | * @return the parent of the alternate unit. |
| 86 | */ |
| 87 | @SuppressWarnings("unchecked") |
| 88 | public final Unit<? super Q> getParent() { |
| 89 | return (Unit<? super Q>) _parent; |
| 90 | } |
| 91 | |
| 92 | @Override |
| 93 | public final Unit<? super Q> getStandardUnit() { |
| 94 | return this; |
| 95 | } |
| 96 | |
| 97 | @Override |
| 98 | public final UnitConverter toStandardUnit() { |
| 99 | return UnitConverter.IDENTITY; |
| 100 | } |
| 101 | |
| 102 | /** |
| 103 | * Indicates if this alternate unit is considered equals to the specified |
| 104 | * object (both are alternate units with equal symbol, equal base units |
| 105 | * and equal converter to base units). |
| 106 | * |
| 107 | * @param that the object to compare for equality. |
| 108 | * @return <code>true</code> if <code>this</code> and <code>that</code> |
| 109 | * are considered equals; <code>false</code>otherwise. |
| 110 | */ |
| 111 | public boolean equals(Object that) { |
| 112 | if (this == that) |
| 113 | return true; |
| 114 | if (!(that instanceof AlternateUnit)) |
| 115 | return false; |
| 116 | AlternateUnit<?> thatUnit = (AlternateUnit<?>) that; |
| 117 | return this._symbol.equals(thatUnit._symbol); // Symbols are unique. |
| 118 | } |
| 119 | |
| 120 | // Implements abstract method. |
| 121 | public int hashCode() { |
| 122 | return _symbol.hashCode(); |
| 123 | } |
| 124 | |
| 125 | private static final long serialVersionUID = 1L; |
| 126 | } |