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| 1 | /* | ||
| 2 | * Copyright (c) 1997, 2006, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | |||
| 28 | /** | ||
| 29 | * This class provides a skeletal implementation of the <tt>Set</tt> | ||
| 30 | * interface to minimize the effort required to implement this | ||
| 31 | * interface. <p> | ||
| 32 | * | ||
| 33 | * The process of implementing a set by extending this class is identical | ||
| 34 | * to that of implementing a Collection by extending AbstractCollection, | ||
| 35 | * except that all of the methods and constructors in subclasses of this | ||
| 36 | * class must obey the additional constraints imposed by the <tt>Set</tt> | ||
| 37 | * interface (for instance, the add method must not permit addition of | ||
| 38 | * multiple instances of an object to a set).<p> | ||
| 39 | * | ||
| 40 | * Note that this class does not override any of the implementations from | ||
| 41 | * the <tt>AbstractCollection</tt> class. It merely adds implementations | ||
| 42 | * for <tt>equals</tt> and <tt>hashCode</tt>.<p> | ||
| 43 | * | ||
| 44 | * This class is a member of the | ||
| 45 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 46 | * Java Collections Framework</a>. | ||
| 47 | * | ||
| 48 | * @param <E> the type of elements maintained by this set | ||
| 49 | * | ||
| 50 | * @author Josh Bloch | ||
| 51 | * @author Neal Gafter | ||
| 52 | * @see Collection | ||
| 53 | * @see AbstractCollection | ||
| 54 | * @see Set | ||
| 55 | * @since 1.2 | ||
| 56 | */ | ||
| 57 | |||
| 58 | public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> { | ||
| 59 | /** | ||
| 60 | * Sole constructor. (For invocation by subclass constructors, typically | ||
| 61 | * implicit.) | ||
| 62 | */ | ||
| 63 | protected AbstractSet() { | ||
| 64 | } | ||
| 65 | |||
| 66 | // Comparison and hashing | ||
| 67 | |||
| 68 | /** | ||
| 69 | * Compares the specified object with this set for equality. Returns | ||
| 70 | * <tt>true</tt> if the given object is also a set, the two sets have | ||
| 71 | * the same size, and every member of the given set is contained in | ||
| 72 | * this set. This ensures that the <tt>equals</tt> method works | ||
| 73 | * properly across different implementations of the <tt>Set</tt> | ||
| 74 | * interface.<p> | ||
| 75 | * | ||
| 76 | * This implementation first checks if the specified object is this | ||
| 77 | * set; if so it returns <tt>true</tt>. Then, it checks if the | ||
| 78 | * specified object is a set whose size is identical to the size of | ||
| 79 | * this set; if not, it returns false. If so, it returns | ||
| 80 | * <tt>containsAll((Collection) o)</tt>. | ||
| 81 | * | ||
| 82 | * @param o object to be compared for equality with this set | ||
| 83 | * @return <tt>true</tt> if the specified object is equal to this set | ||
| 84 | */ | ||
| 85 | public boolean equals(Object o) { | ||
| 86 | if (o == this) | ||
| 87 | return true; | ||
| 88 | |||
| 89 | if (!(o instanceof Set)) | ||
| 90 | return false; | ||
| 91 | Collection c = (Collection) o; | ||
| 92 | if (c.size() != size()) | ||
| 93 | return false; | ||
| 94 | try { | ||
| 95 | return containsAll(c); | ||
| 96 | } catch (ClassCastException unused) { | ||
| 97 | return false; | ||
| 98 | } catch (NullPointerException unused) { | ||
| 99 | return false; | ||
| 100 | } | ||
| 101 | } | ||
| 102 | |||
| 103 | /** | ||
| 104 | * Returns the hash code value for this set. The hash code of a set is | ||
| 105 | * defined to be the sum of the hash codes of the elements in the set, | ||
| 106 | * where the hash code of a <tt>null</tt> element is defined to be zero. | ||
| 107 | * This ensures that <tt>s1.equals(s2)</tt> implies that | ||
| 108 | * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt> | ||
| 109 | * and <tt>s2</tt>, as required by the general contract of | ||
| 110 | * {@link Object#hashCode}. | ||
| 111 | * | ||
| 112 | * <p>This implementation iterates over the set, calling the | ||
| 113 | * <tt>hashCode</tt> method on each element in the set, and adding up | ||
| 114 | * the results. | ||
| 115 | * | ||
| 116 | * @return the hash code value for this set | ||
| 117 | * @see Object#equals(Object) | ||
| 118 | * @see Set#equals(Object) | ||
| 119 | */ | ||
| 120 | public int hashCode() { | ||
| 121 | int h = 0; | ||
| 122 | Iterator<E> i = iterator(); | ||
| 123 | while (i.hasNext()) { | ||
| 124 | E obj = i.next(); | ||
| 125 | if (obj != null) | ||
| 126 | h += obj.hashCode(); | ||
| 127 | } | ||
| 128 | return h; | ||
| 129 | } | ||
| 130 | |||
| 131 | /** | ||
| 132 | * Removes from this set all of its elements that are contained in the | ||
| 133 | * specified collection (optional operation). If the specified | ||
| 134 | * collection is also a set, this operation effectively modifies this | ||
| 135 | * set so that its value is the <i>asymmetric set difference</i> of | ||
| 136 | * the two sets. | ||
| 137 | * | ||
| 138 | * <p>This implementation determines which is the smaller of this set | ||
| 139 | * and the specified collection, by invoking the <tt>size</tt> | ||
| 140 | * method on each. If this set has fewer elements, then the | ||
| 141 | * implementation iterates over this set, checking each element | ||
| 142 | * returned by the iterator in turn to see if it is contained in | ||
| 143 | * the specified collection. If it is so contained, it is removed | ||
| 144 | * from this set with the iterator's <tt>remove</tt> method. If | ||
| 145 | * the specified collection has fewer elements, then the | ||
| 146 | * implementation iterates over the specified collection, removing | ||
| 147 | * from this set each element returned by the iterator, using this | ||
| 148 | * set's <tt>remove</tt> method. | ||
| 149 | * | ||
| 150 | * <p>Note that this implementation will throw an | ||
| 151 | * <tt>UnsupportedOperationException</tt> if the iterator returned by the | ||
| 152 | * <tt>iterator</tt> method does not implement the <tt>remove</tt> method. | ||
| 153 | * | ||
| 154 | * @param c collection containing elements to be removed from this set | ||
| 155 | * @return <tt>true</tt> if this set changed as a result of the call | ||
| 156 | * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation | ||
| 157 | * is not supported by this set | ||
| 158 | * @throws ClassCastException if the class of an element of this set | ||
| 159 | * is incompatible with the specified collection | ||
| 160 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 161 | * @throws NullPointerException if this set contains a null element and the | ||
| 162 | * specified collection does not permit null elements | ||
| 163 | * (<a href="Collection.html#optional-restrictions">optional</a>), | ||
| 164 | * or if the specified collection is null | ||
| 165 | * @see #remove(Object) | ||
| 166 | * @see #contains(Object) | ||
| 167 | */ | ||
| 168 | public boolean removeAll(Collection<?> c) { | ||
| 169 | boolean modified = false; | ||
| 170 | |||
| 171 | if (size() > c.size()) { | ||
| 172 | for (Iterator<?> i = c.iterator(); i.hasNext(); ) | ||
| 173 | modified |= remove(i.next()); | ||
| 174 | } else { | ||
| 175 | for (Iterator<?> i = iterator(); i.hasNext(); ) { | ||
| 176 | if (c.contains(i.next())) { | ||
| 177 | i.remove(); | ||
| 178 | modified = true; | ||
| 179 | } | ||
| 180 | } | ||
| 181 | } | ||
| 182 | return modified; | ||
| 183 | } | ||
| 184 | |||
| 185 | } | ||