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`java.lang.Object`

`java.util.AbstractCollection<E>`

`java.util.AbstractSet<E>`

`java.util.HashSet<T>`

`java.util.LinkedHashSet<T>`

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

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`

public LinkedHashSet()

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

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

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

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.
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