HashSet.java revision 3909
3909N/A * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved. 0N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 0N/A * This code is free software; you can redistribute it and/or modify it 0N/A * under the terms of the GNU General Public License version 2 only, as 2362N/A * published by the Free Software Foundation. Oracle designates this 0N/A * particular file as subject to the "Classpath" exception as provided 2362N/A * by Oracle in the LICENSE file that accompanied this code. 0N/A * This code is distributed in the hope that it will be useful, but WITHOUT 0N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 0N/A * version 2 for more details (a copy is included in the LICENSE file that 0N/A * accompanied this code). 0N/A * You should have received a copy of the GNU General Public License version 0N/A * 2 along with this work; if not, write to the Free Software Foundation, 0N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 2362N/A * or visit www.oracle.com if you need additional information or have any 0N/A * This class implements the <tt>Set</tt> interface, backed by a hash table 0N/A * (actually a <tt>HashMap</tt> instance). It makes no guarantees as to the 0N/A * iteration order of the set; in particular, it does not guarantee that the 0N/A * order will remain constant over time. This class permits the <tt>null</tt> 0N/A * <p>This class offers constant time performance for the basic operations 0N/A * (<tt>add</tt>, <tt>remove</tt>, <tt>contains</tt> and <tt>size</tt>), 0N/A * assuming the hash function disperses the elements properly among the 0N/A * buckets. Iterating over this set requires time proportional to the sum of 0N/A * the <tt>HashSet</tt> instance's size (the number of elements) plus the 0N/A * "capacity" of the backing <tt>HashMap</tt> instance (the number of 0N/A * buckets). Thus, it's very important not to set the initial capacity too 0N/A * high (or the load factor too low) if iteration performance is important. 0N/A * <p><strong>Note that this implementation is not synchronized.</strong> 0N/A * If multiple threads access a hash set concurrently, and at least one of 0N/A * the threads modifies the set, it <i>must</i> be synchronized externally. 0N/A * This is typically accomplished by synchronizing on some object that 0N/A * naturally encapsulates the set. 0N/A * If no such object exists, the set should be "wrapped" using the 0N/A * {@link Collections#synchronizedSet Collections.synchronizedSet} 0N/A * method. This is best done at creation time, to prevent accidental 0N/A * unsynchronized access to the set:<pre> 0N/A * Set s = Collections.synchronizedSet(new HashSet(...));</pre> 0N/A * <p>The iterators returned by this class's <tt>iterator</tt> method are 0N/A * <i>fail-fast</i>: if the set is modified at any time after the iterator is 0N/A * created, in any way except through the iterator's own <tt>remove</tt> 0N/A * method, the Iterator throws a {@link ConcurrentModificationException}. 0N/A * Thus, in the face of concurrent modification, the iterator fails quickly 0N/A * and cleanly, rather than risking arbitrary, non-deterministic behavior at 0N/A * an undetermined time in the future. 0N/A * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 0N/A * as it is, generally speaking, impossible to make any hard guarantees in the 0N/A * presence of unsynchronized concurrent modification. Fail-fast iterators 0N/A * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 0N/A * Therefore, it would be wrong to write a program that depended on this 0N/A * exception for its correctness: <i>the fail-fast behavior of iterators 0N/A * should be used only to detect bugs.</i> 0N/A * <p>This class is a member of the 0N/A * Java Collections Framework</a>. 0N/A * @param <E> the type of elements maintained by this set 0N/A * @author Josh Bloch 0N/A * @author Neal Gafter 0N/A // Dummy value to associate with an Object in the backing Map 0N/A * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has 0N/A * default initial capacity (16) and load factor (0.75). 0N/A * Constructs a new set containing the elements in the specified 0N/A * collection. The <tt>HashMap</tt> is created with default load factor 0N/A * (0.75) and an initial capacity sufficient to contain the elements in 0N/A * the specified collection. 0N/A * @param c the collection whose elements are to be placed into this set 0N/A * @throws NullPointerException if the specified collection is null 0N/A * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has 0N/A * the specified initial capacity and the specified load factor. 0N/A * @param initialCapacity the initial capacity of the hash map 0N/A * @param loadFactor the load factor of the hash map 0N/A * @throws IllegalArgumentException if the initial capacity is less 0N/A * than zero, or if the load factor is nonpositive 0N/A * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has 0N/A * the specified initial capacity and default load factor (0.75). 0N/A * @param initialCapacity the initial capacity of the hash table 0N/A * @throws IllegalArgumentException if the initial capacity is less 0N/A * Constructs a new, empty linked hash set. (This package private 0N/A * constructor is only used by LinkedHashSet.) The backing 0N/A * HashMap instance is a LinkedHashMap with the specified initial 0N/A * capacity and the specified load factor. 0N/A * @param initialCapacity the initial capacity of the hash map 0N/A * @param loadFactor the load factor of the hash map 0N/A * @param dummy ignored (distinguishes this 0N/A * constructor from other int, float constructor.) 0N/A * @throws IllegalArgumentException if the initial capacity is less 0N/A * than zero, or if the load factor is nonpositive 0N/A * Returns an iterator over the elements in this set. The elements 0N/A * are returned in no particular order. 0N/A * @return an Iterator over the elements in this set 0N/A * @see ConcurrentModificationException 0N/A * Returns the number of elements in this set (its cardinality). 0N/A * @return the number of elements in this set (its cardinality) 0N/A * Returns <tt>true</tt> if this set contains no elements. 0N/A * @return <tt>true</tt> if this set contains no elements 0N/A * Returns <tt>true</tt> if this set contains the specified element. 0N/A * More formally, returns <tt>true</tt> if and only if this set 0N/A * contains an element <tt>e</tt> such that 0N/A * <tt>(o==null ? e==null : o.equals(e))</tt>. 0N/A * @param o element whose presence in this set is to be tested 0N/A * @return <tt>true</tt> if this set contains the specified element 0N/A * Adds the specified element to this set if it is not already present. 0N/A * More formally, adds the specified element <tt>e</tt> to this set if 0N/A * this set contains no element <tt>e2</tt> such that 0N/A * <tt>(e==null ? e2==null : e.equals(e2))</tt>. 0N/A * If this set already contains the element, the call leaves the set 0N/A * unchanged and returns <tt>false</tt>. 0N/A * @param e element to be added to this set 0N/A * @return <tt>true</tt> if this set did not already contain the specified 0N/A * Removes the specified element from this set if it is present. 0N/A * More formally, removes an element <tt>e</tt> such that 0N/A * <tt>(o==null ? e==null : o.equals(e))</tt>, 0N/A * if this set contains such an element. Returns <tt>true</tt> if 0N/A * this set contained the element (or equivalently, if this set 0N/A * changed as a result of the call). (This set will not contain the 0N/A * element once the call returns.) 0N/A * @param o object to be removed from this set, if present 0N/A * @return <tt>true</tt> if the set contained the specified element 0N/A * Removes all of the elements from this set. 0N/A * The set will be empty after this call returns. 0N/A * Returns a shallow copy of this <tt>HashSet</tt> instance: the elements 0N/A * themselves are not cloned. 0N/A * @return a shallow copy of this set 0N/A * Save the state of this <tt>HashSet</tt> instance to a stream (that is, 0N/A * @serialData The capacity of the backing <tt>HashMap</tt> instance 0N/A * (int), and its load factor (float) are emitted, followed by 0N/A * the size of the set (the number of elements it contains) 0N/A * (int), followed by all of its elements (each an Object) in 0N/A * no particular order. 0N/A // Write out any hidden serialization magic 0N/A // Write out HashMap capacity and load factor 0N/A // Write out all elements in the proper order. 0N/A * Reconstitute the <tt>HashSet</tt> instance from a stream (that is, 0N/A // Read in any hidden serialization magic 0N/A // Read in HashMap capacity and load factor and create backing HashMap 0N/A // Read in all elements in the proper order.