gnu.trove.impl.hash

Class THash

java.lang.Object

gnu.trove.impl.hash.THash

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable

Direct Known Subclasses:

TObjectHash, TPrimitiveHash

public abstract class THash
extends java.lang.Object
implements java.io.Externalizable

Base class for hashtables that use open addressing to resolve collisions. Created: Wed Nov 28 21:11:16 2001

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
THash() Creates a new THash instance with the default capacity and load factor.
THash(int initialCapacity) Creates a new THash instance with a prime capacity at or near the specified capacity and with the default load factor.
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.

Method Summary

Modifier and Type	Method and Description
abstract int	capacity()
void	clear() Empties the collection.
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.
void	ensureCapacity(int desiredCapacity) Ensure that this hashtable has sufficient capacity to hold desiredCapacity additional elements without requiring a rehash.
float	getAutoCompactionFactor()
boolean	isEmpty() Tells whether this set is currently holding any elements.
void	readExternal(java.io.ObjectInput in)
void	reenableAutoCompaction(boolean check_for_compaction) Re-enable auto-compaction after it was disabled via tempDisableAutoCompaction().
void	setAutoCompactionFactor(float factor) The auto-compaction factor controls whether and when a table performs a compact() automatically after a certain number of remove operations.
int	size() Returns the number of distinct elements in this collection.
void	tempDisableAutoCompaction() Temporarily disables auto-compaction.
void	trimToSize() This simply calls compact.
void	writeExternal(java.io.ObjectOutput out)

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

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.

Parameters:

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.

Parameters:

initialCapacity - an int value

loadFactor - a float value

Method Detail

isEmpty

public boolean isEmpty()

Tells whether this set is currently holding any elements.

Returns:

a boolean value

size

public int size()

Returns the number of distinct elements in this collection.

Returns:

an int value

capacity

public abstract int capacity()

Returns:

the current physical capacity of the hash 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.

Parameters:

desiredCapacity - an int value

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:

1. You'll free memory allocated to the table but no longer needed because of the remove()s.
2. 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.

setAutoCompactionFactor

public void setAutoCompactionFactor(float factor)

The auto-compaction factor controls whether and when a table performs a compact() automatically 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.

Parameters:

factor - a float that indicates the auto-compaction factor

getAutoCompactionFactor

public float getAutoCompactionFactor()

Returns:

a <float that represents the auto-compaction factor.

See Also:

setAutoCompactionFactor(float)

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.

See Also:

compact()

clear

public void clear()

Empties the collection.

tempDisableAutoCompaction

public void tempDisableAutoCompaction()

Temporarily disables auto-compaction. MUST be followed by calling reenableAutoCompaction(boolean).

reenableAutoCompaction

public void reenableAutoCompaction(boolean check_for_compaction)

Re-enable auto-compaction after it was disabled via tempDisableAutoCompaction().

Parameters:

check_for_compaction - True if compaction should be performed if needed before returning. If false, no compaction will be performed.

writeExternal

public void writeExternal(java.io.ObjectOutput out)
                   throws java.io.IOException

Specified by:

writeExternal in interface java.io.Externalizable

Throws:

java.io.IOException

readExternal

public void readExternal(java.io.ObjectInput in)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException

Specified by:

readExternal in interface java.io.Externalizable

Throws:

java.io.IOException

java.lang.ClassNotFoundException