Source Code Cross Referenced for AbstractSet.java in  » 6.0-JDK-Core » Collections-Jar-Zip-Logging-regex » java » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » 6.0 JDK Core » Collections Jar Zip Logging regex » java.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


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        }
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