1 /*
2 * Copyright 1997-2006 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any 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 (optional)
160 * @throws NullPointerException if this set contains a null element and the
161 * specified collection does not permit null elements (optional),
162 * or if the specified collection is null
163 * @see #remove(Object)
164 * @see #contains(Object)
165 */
166 public boolean removeAll(Collection<?> c) {
167 boolean modified = false;
168
169 if (size() > c.size()) {
170 for (Iterator<?> i = c.iterator(); i.hasNext(); )
171 modified |= remove(i.next());
172 } else {
173 for (Iterator<?> i = iterator(); i.hasNext(); ) {
174 if (c.contains(i.next())) {
175 i.remove();
176 modified = true;
177 }
178 }
179 }
180 return modified;
181 }
182
183 }
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