java.util

Class LinkedHashSet<T>

Implemented Interfaces:
Cloneable, Collection<E>, Iterable<E>, Serializable, Set<E>

public class LinkedHashSet<T>
extends HashSet<T>
implements Set<E>, Cloneable, Serializable

This class provides a hashtable-backed implementation of the Set interface, with predictable traversal order.

It uses a hash-bucket approach; that is, hash collisions are handled by linking the new node off of the pre-existing node (or list of nodes). In this manner, techniques such as linear probing (which can cause primary clustering) and rehashing (which does not fit very well with Java's method of precomputing hash codes) are avoided. In addition, this maintains a doubly-linked list which tracks insertion order. Note that the insertion order is not modified if an add simply reinserts an element in the set.

One of the nice features of tracking insertion order is that you can copy a set, and regardless of the implementation of the original, produce the same results when iterating over the copy. This is possible without needing the overhead of TreeSet.

Under ideal circumstances (no collisions), LinkedHashSet offers O(1) performance on most operations. In the worst case (all elements map to the same hash code -- very unlikely), most operations are O(n).

LinkedHashSet accepts the null entry. It is not synchronized, so if you need multi-threaded access, consider using:
Set s = Collections.synchronizedSet(new LinkedHashSet(...));

The iterators are fail-fast, meaning that any structural modification, except for remove() called on the iterator itself, cause the iterator to throw a ConcurrentModificationException rather than exhibit non-deterministic behavior.

Since:
1.4
See Also:
Object.hashCode(), Collection, Set, HashSet, TreeSet, Collections.synchronizedSet(Set), Serialized Form

Constructor Summary

LinkedHashSet()
Construct a new, empty HashSet whose backing HashMap has the default capacity (11) and loadFactor (0.75).
LinkedHashSet(T> c)
Construct a new HashSet with the same elements as are in the supplied collection (eliminating any duplicates, of course).
LinkedHashSet(int initialCapacity)
Construct a new, empty HashSet whose backing HashMap has the supplied capacity and the default load factor (0.75).
LinkedHashSet(int initialCapacity, float loadFactor)
Construct a new, empty HashSet whose backing HashMap has the supplied capacity and load factor.

Method Summary

Methods inherited from class java.util.HashSet<T>

add, clear, clone, contains, isEmpty, iterator, remove, size

Methods inherited from class java.util.AbstractSet<E>

equals, hashCode, removeAll

Methods inherited from class java.util.AbstractCollection<E>

T[] toArray, add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toString

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LinkedHashSet

public LinkedHashSet()
Construct a new, empty HashSet whose backing HashMap has the default capacity (11) and loadFactor (0.75).

LinkedHashSet

public LinkedHashSet(T> c)
Construct a new HashSet with the same elements as are in the supplied collection (eliminating any duplicates, of course). The backing storage has twice the size of the collection, or the default size of 11, whichever is greater; and the default load factor (0.75).
Parameters:
c - a collection of initial set elements
Throws:
NullPointerException - if c is null

LinkedHashSet

public LinkedHashSet(int initialCapacity)
Construct a new, empty HashSet whose backing HashMap has the supplied capacity and the default load factor (0.75).
Parameters:
initialCapacity - the initial capacity of the backing HashMap
Throws:
IllegalArgumentException - if the capacity is negative

LinkedHashSet

public LinkedHashSet(int initialCapacity,
                     float loadFactor)
Construct a new, empty HashSet whose backing HashMap has the supplied capacity and load factor.
Parameters:
initialCapacity - the initial capacity of the backing HashMap
loadFactor - the load factor of the backing HashMap
Throws:
IllegalArgumentException - if either argument is negative, or if loadFactor is POSITIVE_INFINITY or NaN

LinkedHashSet.java -- a set backed by a LinkedHashMap, for linked list traversal. Copyright (C) 2001, 2004, 2005, 2007 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.