001 /*
002 * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package java.util;
027
028 /**
029 * This class provides a skeletal implementation of the <tt>Set</tt>
030 * interface to minimize the effort required to implement this
031 * interface. <p>
032 *
033 * The process of implementing a set by extending this class is identical
034 * to that of implementing a Collection by extending AbstractCollection,
035 * except that all of the methods and constructors in subclasses of this
036 * class must obey the additional constraints imposed by the <tt>Set</tt>
037 * interface (for instance, the add method must not permit addition of
038 * multiple instances of an object to a set).<p>
039 *
040 * Note that this class does not override any of the implementations from
041 * the <tt>AbstractCollection</tt> class. It merely adds implementations
042 * for <tt>equals</tt> and <tt>hashCode</tt>.<p>
043 *
044 * This class is a member of the
045 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
046 * Java Collections Framework</a>.
047 *
048 * @param <E> the type of elements maintained by this set
049 *
050 * @author Josh Bloch
051 * @author Neal Gafter
052 * @version 1.35, 05/05/07
053 * @see Collection
054 * @see AbstractCollection
055 * @see Set
056 * @since 1.2
057 */
058
059 public abstract class AbstractSet<E> extends AbstractCollection<E>
060 implements Set<E> {
061 /**
062 * Sole constructor. (For invocation by subclass constructors, typically
063 * implicit.)
064 */
065 protected AbstractSet() {
066 }
067
068 // Comparison and hashing
069
070 /**
071 * Compares the specified object with this set for equality. Returns
072 * <tt>true</tt> if the given object is also a set, the two sets have
073 * the same size, and every member of the given set is contained in
074 * this set. This ensures that the <tt>equals</tt> method works
075 * properly across different implementations of the <tt>Set</tt>
076 * interface.<p>
077 *
078 * This implementation first checks if the specified object is this
079 * set; if so it returns <tt>true</tt>. Then, it checks if the
080 * specified object is a set whose size is identical to the size of
081 * this set; if not, it returns false. If so, it returns
082 * <tt>containsAll((Collection) o)</tt>.
083 *
084 * @param o object to be compared for equality with this set
085 * @return <tt>true</tt> if the specified object is equal to this set
086 */
087 public boolean equals(Object o) {
088 if (o == this )
089 return true;
090
091 if (!(o instanceof Set))
092 return false;
093 Collection c = (Collection) o;
094 if (c.size() != size())
095 return false;
096 try {
097 return containsAll(c);
098 } catch (ClassCastException unused) {
099 return false;
100 } catch (NullPointerException unused) {
101 return false;
102 }
103 }
104
105 /**
106 * Returns the hash code value for this set. The hash code of a set is
107 * defined to be the sum of the hash codes of the elements in the set,
108 * where the hash code of a <tt>null</tt> element is defined to be zero.
109 * This ensures that <tt>s1.equals(s2)</tt> implies that
110 * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
111 * and <tt>s2</tt>, as required by the general contract of
112 * {@link Object#hashCode}.
113 *
114 * <p>This implementation iterates over the set, calling the
115 * <tt>hashCode</tt> method on each element in the set, and adding up
116 * the results.
117 *
118 * @return the hash code value for this set
119 * @see Object#equals(Object)
120 * @see Set#equals(Object)
121 */
122 public int hashCode() {
123 int h = 0;
124 Iterator<E> i = iterator();
125 while (i.hasNext()) {
126 E obj = i.next();
127 if (obj != null)
128 h += obj.hashCode();
129 }
130 return h;
131 }
132
133 /**
134 * Removes from this set all of its elements that are contained in the
135 * specified collection (optional operation). If the specified
136 * collection is also a set, this operation effectively modifies this
137 * set so that its value is the <i>asymmetric set difference</i> of
138 * the two sets.
139 *
140 * <p>This implementation determines which is the smaller of this set
141 * and the specified collection, by invoking the <tt>size</tt>
142 * method on each. If this set has fewer elements, then the
143 * implementation iterates over this set, checking each element
144 * returned by the iterator in turn to see if it is contained in
145 * the specified collection. If it is so contained, it is removed
146 * from this set with the iterator's <tt>remove</tt> method. If
147 * the specified collection has fewer elements, then the
148 * implementation iterates over the specified collection, removing
149 * from this set each element returned by the iterator, using this
150 * set's <tt>remove</tt> method.
151 *
152 * <p>Note that this implementation will throw an
153 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
154 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method.
155 *
156 * @param c collection containing elements to be removed from this set
157 * @return <tt>true</tt> if this set changed as a result of the call
158 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
159 * is not supported by this set
160 * @throws ClassCastException if the class of an element of this set
161 * is incompatible with the specified collection (optional)
162 * @throws NullPointerException if this set contains a null element and the
163 * specified collection does not permit null elements (optional),
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 }
|