1 | /*
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2 | * GeoTools - The Open Source Java GIS Toolkit
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3 | * http://geotools.org
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4 | *
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5 | * (C) 2001-2008, Open Source Geospatial Foundation (OSGeo)
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6 | *
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7 | * This library is free software; you can redistribute it and/or
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8 | * modify it under the terms of the GNU Lesser General Public
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9 | * License as published by the Free Software Foundation;
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10 | * version 2.1 of the License.
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11 | *
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12 | * This library is distributed in the hope that it will be useful,
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13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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15 | * Lesser General Public License for more details.
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16 | */
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17 | package org.geotools.util;
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18 |
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19 |
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20 | /**
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21 | * A canonical set of objects, used to optimize memory use.
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22 | * The operation of this set is similar in spirit to the {@link String#intern} method.
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23 | * The following example shows a convenient way to use {@code CanonicalSet} as an
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24 | * internal pool of immutable objects.
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25 | *
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26 | * <blockquote><pre>
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27 | * public Foo create(String definition) {
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28 | * Foo created = new Foo(definition);
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29 | * return (Foo) canonicalSet.unique(created);
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30 | * }
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31 | * </pre></blockquote>
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32 | *
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33 | * The {@code CanonicalSet} has a {@link #get} method that is not part of the {@link java.util.Set}
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34 | * interface. This {@code get} method retrieves an entry from this set that is equals to
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35 | * the supplied object. The {@link #unique} method combines a {@code get} followed by a
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36 | * {@code put} operation if the specified object was not in the set.
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37 | * <p>
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38 | * The set of objects is held by weak references as explained in {@link WeakHashSet}.
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39 | * The {@code CanonicalSet} class is thread-safe.
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40 | *
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41 | * @param <E> The type of elements in the set.
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42 | *
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43 | * @since 2.4
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44 | *
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45 | * @source $URL: http://svn.osgeo.org/geotools/branches/2.7.x/modules/library/metadata/src/main/java/org/geotools/util/CanonicalSet.java $
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46 | * @version $Id: CanonicalSet.java 37298 2011-05-25 05:16:15Z mbedward $
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47 | * @author Martin Desruisseaux (IRD)
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48 | * @author Jody Garnett
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49 | */
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50 | public class CanonicalSet<E> extends WeakHashSet<E> {
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51 | /**
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52 | * Constructs a {@code CanonicalSet}.
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53 | *
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54 | * @deprecated Use {@link #newInstance} instead.
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55 | */
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56 | public CanonicalSet() {
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57 | }
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58 |
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59 | /**
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60 | * Constructs a {@code CanonicalSet} for elements of the specified type.
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61 | *
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62 | * @param type The type of elements in the set.
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63 | *
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64 | * @since 2.5
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65 | */
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66 | protected CanonicalSet(final Class<E> type) {
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67 | super(type);
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68 | }
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69 |
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70 | /**
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71 | * Constructs a {@code CanonicalSet} for elements of the specified type.
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72 | *
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73 | * @param <E> The type of elements in the set.
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74 | * @param type The type of elements in the set.
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75 | * @return An initially empty set for elements of the given type.
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76 | *
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77 | * @since 2.5
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78 | */
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79 | public static <E> CanonicalSet<E> newInstance(final Class<E> type) {
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80 | return new CanonicalSet<E>(type);
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81 | }
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82 |
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83 | /**
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84 | * Returns an object equals to {@code object} if such an object already exist in this
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85 | * {@code CanonicalSet}. Otherwise, adds {@code object} to this {@code CanonicalSet}.
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86 | * This method is equivalents to the following code:
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87 | *
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88 | * <blockquote><pre>
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89 | * if (object != null) {
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90 | * Object current = get(object);
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91 | * if (current != null) {
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92 | * return current;
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93 | * } else {
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94 | * add(object);
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95 | * }
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96 | * }
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97 | * return object;
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98 | * </pre></blockquote>
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99 | *
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100 | * @param <T> The type of the element to get.
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101 | * @param object The element to get or to add in the set if not already presents.
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102 | * @return An element equals to the given one if already presents in the set,
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103 | * or the given {@code object} otherwise.
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104 | */
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105 | public synchronized <T extends E> T unique(final T object) {
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106 | return intern(object, INTERN);
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107 | }
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108 | }
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