THash instance with the default
+ * capacity and load factor.
+ */
+ public THash() {
+ this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * Creates a new THash instance with a prime capacity
+ * at or near the specified capacity and with the default load
+ * factor.
+ *
+ * @param initialCapacity an int value
+ */
+ public THash(int initialCapacity) {
+ this(initialCapacity, DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * 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.
+ *
+ * @param initialCapacity an int value
+ * @param loadFactor a float value
+ */
+ public THash(int initialCapacity, float loadFactor) {
+ super();
+ _loadFactor = loadFactor;
+
+ // Through testing, the load factor (especially the default load factor) has been
+ // found to be a pretty good starting auto-compaction factor.
+ _autoCompactionFactor = loadFactor;
+
+ setUp(HashFunctions.fastCeil(initialCapacity / loadFactor));
+ }
+
+ public Object clone() {
+ try {
+ return super.clone();
+ } catch (CloneNotSupportedException cnse) {
+ return null; // it's supported
+ }
+ }
+
+ /**
+ * Tells whether this set is currently holding any elements.
+ *
+ * @return a boolean value
+ */
+ public boolean isEmpty() {
+ return 0 == _size;
+ }
+
+ /**
+ * Returns the number of distinct elements in this collection.
+ *
+ * @return an int value
+ */
+ public int size() {
+ return _size;
+ }
+
+ /**
+ * @return the current physical capacity of the hash table.
+ */
+ abstract protected int capacity();
+
+ /**
+ * 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.
+ *
+ * @param desiredCapacity an int value
+ */
+ public void ensureCapacity(int desiredCapacity) {
+ if (desiredCapacity > (_maxSize - size())) {
+ rehash(PrimeFinder.nextPrime(HashFunctions.fastCeil(
+ (desiredCapacity + size()) / _loadFactor) + 1));
+ computeMaxSize(capacity());
+ }
+ }
+
+ /**
+ * 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:
+ *
+ *
+ * Setting this value to zero will disable auto-compaction.
+ */
+ public void setAutoCompactionFactor( float factor ) {
+ if ( factor < 0 ) {
+ throw new IllegalArgumentException( "Factor must be >= 0: " + factor );
+ }
+
+ _autoCompactionFactor = factor;
+ }
+
+ /**
+ * @see #setAutoCompactionFactor
+ */
+ public float getAutoCompactionFactor() {
+ return _autoCompactionFactor;
+ }
+
+
+ /**
+ * This simply calls {@link #compact 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 #compact
+ */
+ public final void trimToSize() {
+ compact();
+ }
+
+ /**
+ * Delete the record at index. Reduces the size of the
+ * collection by one.
+ *
+ * @param index an int value
+ */
+ protected void removeAt(int index) {
+ _size--;
+
+ // If auto-compaction is enabled, see if we need to compact
+ if ( _autoCompactionFactor != 0 ) {
+ _autoCompactRemovesRemaining--;
+
+ if ( !_autoCompactTemporaryDisable && _autoCompactRemovesRemaining <= 0 ) {
+ // Do the compact
+ // NOTE: this will cause the next compaction interval to be calculated
+ compact();
+ }
+ }
+ }
+
+ /**
+ * Empties the collection.
+ */
+ public void clear() {
+ _size = 0;
+ _free = capacity();
+ }
+
+ /**
+ * initializes the hashtable to a prime capacity which is at least
+ * initialCapacity + 1.
+ *
+ * @param initialCapacity an int value
+ * @return the actual capacity chosen
+ */
+ protected int setUp(int initialCapacity) {
+ int capacity;
+
+ capacity = PrimeFinder.nextPrime(initialCapacity);
+ computeMaxSize(capacity);
+ computeNextAutoCompactionAmount(initialCapacity);
+
+ return capacity;
+ }
+
+ /**
+ * Rehashes the set.
+ *
+ * @param newCapacity an int value
+ */
+ protected abstract void rehash(int newCapacity);
+
+ /**
+ * Temporarily disables auto-compaction. MUST be followed by calling
+ * {@link #reenableAutoCompaction}.
+ */
+ protected void tempDisableAutoCompaction() {
+ _autoCompactTemporaryDisable = true;
+ }
+
+ /**
+ * Re-enable auto-compaction after it was disabled via
+ * {@link #tempDisableAutoCompaction()}.
+ *
+ * @param check_for_compaction True if compaction should be performed if needed
+ * before returning. If false, no compaction will be
+ * performed.
+ */
+ protected void reenableAutoCompaction( boolean check_for_compaction ) {
+ _autoCompactTemporaryDisable = false;
+
+ if ( check_for_compaction && _autoCompactRemovesRemaining <= 0 &&
+ _autoCompactionFactor != 0 ) {
+
+ // Do the compact
+ // NOTE: this will cause the next compaction interval to be calculated
+ compact();
+ }
+ }
+
+
+ /**
+ * Computes the values of maxSize. There will always be at least
+ * one free slot required.
+ *
+ * @param capacity an int value
+ */
+ private void computeMaxSize(int capacity) {
+ // need at least one free slot for open addressing
+ _maxSize = Math.min(capacity - 1, (int) (capacity * _loadFactor));
+ _free = capacity - _size; // reset the free element count
+ }
+
+
+ /**
+ * Computes the number of removes that need to happen before the next auto-compaction
+ * will occur.
+ */
+ private void computeNextAutoCompactionAmount( int size ) {
+ if ( _autoCompactionFactor != 0 ) {
+ // NOTE: doing the round ourselves has been found to be faster than using
+ // Math.round.
+ _autoCompactRemovesRemaining =
+ ( int ) ( ( size * _autoCompactionFactor ) + 0.5f );
+ }
+ }
+
+
+ /**
+ * After an insert, this hook is called to adjust the size/free
+ * values of the set and to perform rehashing if necessary.
+ */
+ protected final void postInsertHook(boolean usedFreeSlot) {
+ if (usedFreeSlot) {
+ _free--;
+ }
+
+ // rehash whenever we exhaust the available space in the table
+ if (++_size > _maxSize || _free == 0) {
+ // choose a new capacity suited to the new state of the table
+ // if we've grown beyond our maximum size, double capacity;
+ // if we've exhausted the free spots, rehash to the same capacity,
+ // which will free up any stale removed slots for reuse.
+ int newCapacity = _size > _maxSize ? PrimeFinder.nextPrime(capacity() << 1) : capacity();
+ rehash(newCapacity);
+ computeMaxSize(capacity());
+ }
+ }
+
+ protected int calculateGrownCapacity() {
+ return capacity() << 1;
+ }
+
+
+ public void writeExternal(ObjectOutput out) throws IOException {
+ // VERSION
+ out.writeByte( 0 );
+
+ // LOAD FACTOR
+ out.writeFloat( _loadFactor );
+
+ // AUTO COMPACTION LOAD FACTOR
+ out.writeFloat( _autoCompactionFactor );
+ }
+
+ public void readExternal(ObjectInput in)
+ throws IOException, ClassNotFoundException {
+
+ // VERSION
+ in.readByte();
+
+ // LOAD FACTOR
+ float old_factor = _loadFactor;
+ _loadFactor = in.readFloat();
+
+ // AUTO COMPACTION LOAD FACTOR
+ _autoCompactionFactor = in.readFloat();
+
+
+ // If we change the laod factor from the default, re-setup
+ if ( old_factor != _loadFactor ) {
+ setUp((int)Math.ceil(DEFAULT_INITIAL_CAPACITY / _loadFactor));
+ }
+ }
+}// THash