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jlechner |
/* LinkedHashSet.java -- a set backed by a LinkedHashMap, for linked
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list traversal.
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Copyright (C) 2001, 2005 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util;
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import java.io.Serializable;
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/**
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* This class provides a hashtable-backed implementation of the
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* Set interface, with predictable traversal order.
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* <p>
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*
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* It uses a hash-bucket approach; that is, hash collisions are handled
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* by linking the new node off of the pre-existing node (or list of
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* nodes). In this manner, techniques such as linear probing (which
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* can cause primary clustering) and rehashing (which does not fit very
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* well with Java's method of precomputing hash codes) are avoided. In
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* addition, this maintains a doubly-linked list which tracks insertion
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* order. Note that the insertion order is not modified if an
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* <code>add</code> simply reinserts an element in the set.
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* <p>
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*
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* One of the nice features of tracking insertion order is that you can
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* copy a set, and regardless of the implementation of the original,
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* produce the same results when iterating over the copy. This is possible
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* without needing the overhead of <code>TreeSet</code>.
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* <p>
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*
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* Under ideal circumstances (no collisions), LinkedHashSet offers O(1)
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* performance on most operations. In the worst case (all elements map
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* to the same hash code -- very unlikely), most operations are O(n).
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* <p>
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*
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* LinkedHashSet accepts the null entry. It is not synchronized, so if
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* you need multi-threaded access, consider using:<br>
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* <code>Set s = Collections.synchronizedSet(new LinkedHashSet(...));</code>
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* <p>
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*
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* The iterators are <i>fail-fast</i>, meaning that any structural
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* modification, except for <code>remove()</code> called on the iterator
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* itself, cause the iterator to throw a
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* {@link ConcurrentModificationException} rather than exhibit
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* non-deterministic behavior.
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*
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* @author Eric Blake (ebb9@email.byu.edu)
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* @see Object#hashCode()
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* @see Collection
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* @see Set
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* @see HashSet
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* @see TreeSet
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* @see Collections#synchronizedSet(Set)
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* @since 1.4
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* @status updated to 1.4
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*/
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public class LinkedHashSet extends HashSet
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implements Set, Cloneable, Serializable
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{
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/**
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* Compatible with JDK 1.4.
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*/
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private static final long serialVersionUID = -2851667679971038690L;
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/**
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* Construct a new, empty HashSet whose backing HashMap has the default
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* capacity (11) and loadFacor (0.75).
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*/
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public LinkedHashSet()
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{
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super();
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}
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/**
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* Construct a new, empty HashSet whose backing HashMap has the supplied
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* capacity and the default load factor (0.75).
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*
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* @param initialCapacity the initial capacity of the backing HashMap
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* @throws IllegalArgumentException if the capacity is negative
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*/
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public LinkedHashSet(int initialCapacity)
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{
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super(initialCapacity);
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}
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/**
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* Construct a new, empty HashSet whose backing HashMap has the supplied
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* capacity and load factor.
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*
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* @param initialCapacity the initial capacity of the backing HashMap
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* @param loadFactor the load factor of the backing HashMap
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* @throws IllegalArgumentException if either argument is negative, or
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* if loadFactor is POSITIVE_INFINITY or NaN
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*/
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public LinkedHashSet(int initialCapacity, float loadFactor)
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{
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super(initialCapacity, loadFactor);
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}
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/**
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* Construct a new HashSet with the same elements as are in the supplied
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* collection (eliminating any duplicates, of course). The backing storage
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* has twice the size of the collection, or the default size of 11,
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* whichever is greater; and the default load factor (0.75).
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*
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* @param c a collection of initial set elements
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* @throws NullPointerException if c is null
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*/
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public LinkedHashSet(Collection c)
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{
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super(c);
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}
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/**
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* Helper method which initializes the backing Map.
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*
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* @param capacity the initial capacity
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* @param load the initial load factor
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* @return the backing HashMap
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*/
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HashMap init(int capacity, float load)
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{
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return new LinkedHashMap(capacity, load);
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}
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}
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