gnu.trove
Class THash
- Cloneable
public abstract class THash
extends java.lang.Object
implements Cloneable
Base class for hashtables that use open addressing to resolve
collisions.
Created: Wed Nov 28 21:11:16 2001
$Id: THash.java,v 1.9 2007/06/29 20:03:10 robeden Exp $- Eric D. Friedman
- Rob Eden (auto-compaction)
protected static int | DEFAULT_INITIAL_CAPACITY - the default initial capacity for the hash table.
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protected static float | DEFAULT_LOAD_FACTOR - the load above which rehashing occurs.
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protected int | _autoCompactRemovesRemaining - The number of removes that should be performed before an auto-compaction occurs.
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protected float | _autoCompactionFactor - The auto-compaction falctor for the table.
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protected int | _free - the current number of free slots in the hash.
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protected float | _loadFactor - Determines how full the internal table can become before
rehashing is required.
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protected int | _maxSize - The maximum number of elements allowed without allocating more
space.
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protected int | _size - the current number of occupied slots in the hash.
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THash() - Creates a new
THash instance with the default
capacity and load factor.
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THash(int initialCapacity) - Creates a new
THash instance with a prime capacity
at or near the specified capacity and with the default load
factor.
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THash(int initialCapacity, float loadFactor) - Creates a new
THash instance with a prime capacity
at or near the minimum needed to hold initialCapacity
elements with load factor loadFactor without triggering
a rehash.
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protected int | calculateGrownCapacity()
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protected abstract int | capacity()
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void | clear() - Empties the collection.
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Object | clone()
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void | compact() - Compresses the hashtable to the minimum prime size (as defined
by PrimeFinder) that will hold all of the elements currently in
the table.
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void | ensureCapacity(int desiredCapacity) - Ensure that this hashtable has sufficient capacity to hold
desiredCapacity additional elements without
requiring a rehash.
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float | getAutoCompactionFactor()
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boolean | isEmpty() - Tells whether this set is currently holding any elements.
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protected void | postInsertHook(boolean usedFreeSlot) - After an insert, this hook is called to adjust the size/free
values of the set and to perform rehashing if necessary.
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protected void | reenableAutoCompaction(boolean check_for_compaction) - Re-enable auto-compaction after it was disabled via
tempDisableAutoCompaction() .
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protected abstract void | rehash(int newCapacity) - Rehashes the set.
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protected void | removeAt(int index) - Delete the record at index.
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void | setAutoCompactionFactor(float factor) - The auto-compaction factor controls whether and when a table performs a
compact() automatcially after a certain number of remove operations.
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protected int | setUp(int initialCapacity) - initializes the hashtable to a prime capacity which is at least
initialCapacity + 1.
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int | size() - Returns the number of distinct elements in this collection.
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protected void | tempDisableAutoCompaction() - Temporarily disables auto-compaction.
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void | trimToSize() - This simply calls
compact .
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DEFAULT_INITIAL_CAPACITY
protected static final int DEFAULT_INITIAL_CAPACITY
the default initial capacity for the hash table. This is one
less than a prime value because one is added to it when
searching for a prime capacity to account for the free slot
required by open addressing. Thus, the real default capacity is
11.
DEFAULT_LOAD_FACTOR
protected static final float DEFAULT_LOAD_FACTOR
the load above which rehashing occurs.
_autoCompactRemovesRemaining
protected int _autoCompactRemovesRemaining
The number of removes that should be performed before an auto-compaction occurs.
_autoCompactionFactor
protected float _autoCompactionFactor
The auto-compaction falctor for the table.
_free
protected int _free
the current number of free slots in the hash.
_loadFactor
protected float _loadFactor
Determines how full the internal table can become before
rehashing is required. This must be a value in the range: 0.0 <10 loadFactor <321.0. The default value is 0.5, which is about as
large as you can get in open addressing without hurting
performance. Cf. Knuth, Volume 3., Chapter 6.
_maxSize
protected int _maxSize
The maximum number of elements allowed without allocating more
space.
_size
protected int _size
the current number of occupied slots in the hash.
THash
public THash()
Creates a new THash
instance with the default
capacity and load factor.
THash
public THash(int initialCapacity)
Creates a new THash
instance with a prime capacity
at or near the specified capacity and with the default load
factor.
initialCapacity
- an int
value
THash
public THash(int initialCapacity,
float loadFactor)
Creates a new THash
instance with a prime capacity
at or near the minimum needed to hold initialCapacity
elements with load factor loadFactor without triggering
a rehash.
initialCapacity
- an int
valueloadFactor
- a float
value
calculateGrownCapacity
protected int calculateGrownCapacity()
capacity
protected abstract int capacity()
- the current physical capacity of the hash table.
clear
public void clear()
Empties the collection.
clone
public Object clone()
compact
public void compact()
Compresses the hashtable to the minimum prime size (as defined
by PrimeFinder) that will hold all of the elements currently in
the table. If you have done a lot of
remove
operations and plan to do a lot of queries or insertions or
iteration, it is a good idea to invoke this method. Doing so
will accomplish two things:
- You'll free memory allocated to the table but no
longer needed because of the remove()s.
- You'll get better query/insert/iterator performance
because there won't be any REMOVED slots to skip
over when probing for indices in the table.
ensureCapacity
public void ensureCapacity(int desiredCapacity)
Ensure that this hashtable has sufficient capacity to hold
desiredCapacity additional elements without
requiring a rehash. This is a tuning method you can call
before doing a large insert.
desiredCapacity
- an int
value
getAutoCompactionFactor
public float getAutoCompactionFactor()
isEmpty
public boolean isEmpty()
Tells whether this set is currently holding any elements.
postInsertHook
protected final void postInsertHook(boolean usedFreeSlot)
After an insert, this hook is called to adjust the size/free
values of the set and to perform rehashing if necessary.
reenableAutoCompaction
protected void reenableAutoCompaction(boolean check_for_compaction)
check_for_compaction
- True if compaction should be performed if needed
before returning. If false, no compaction will be
performed.
rehash
protected abstract void rehash(int newCapacity)
Rehashes the set.
newCapacity
- an int
value
removeAt
protected void removeAt(int index)
Delete the record at index. Reduces the size of the
collection by one.
setAutoCompactionFactor
public void setAutoCompactionFactor(float factor)
The auto-compaction factor controls whether and when a table performs a
compact()
automatcially after a certain number of remove operations.
If the value is non-zero, the number of removes that need to occur for
auto-compaction is the size of table at the time of the previous compaction
(or the initial capacity) multiplied by this factor.
Setting this value to zero will disable auto-compaction.
setUp
protected int setUp(int initialCapacity)
initializes the hashtable to a prime capacity which is at least
initialCapacity + 1.
initialCapacity
- an int
value
- the actual capacity chosen
size
public int size()
Returns the number of distinct elements in this collection.
tempDisableAutoCompaction
protected void tempDisableAutoCompaction()
trimToSize
public final void trimToSize()
This simply calls
compact
. It is included for
symmetry with other collection classes. Note that the name of this
method is somewhat misleading (which is why we prefer
compact) as the load factor may require capacity above
and beyond the size of this collection.
GNU Trove is copyright B) 2001-2007 Eric D. Friedman. All Rights Reserved.