tprimitivehash.java

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///////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2001, Eric D. Friedman All Rights Reserved.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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 Lesser General Public
// License along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
///////////////////////////////////////////////////////////////////////////////

package gnu.trove;

/**
 * The base class for hashtables of primitive values.  Since there is
 * no notion of object equality for primitives, it isn't possible to
 * use a `REMOVED' object to track deletions in an open-addressed table.
 * So, we have to resort to using a parallel `bookkeeping' array of bytes,
 * in which flags can be set to indicate that a particular slot in the
 * hash table is FREE, FULL, or REMOVED.
 *
 * Created: Fri Jan 11 18:55:16 2002
 *
 * @author Eric D. Friedman
 * @version $Id: TPrimitiveHash.java,v 1.1.1.1 2003/07/14 19:36:04 mccallum Exp $
 */

abstract public class TPrimitiveHash extends THash  {
    /** flags indicating whether each position in the hash is
     * FREE, FULL, or REMOVED */
    protected transient byte[] _states;

    /* constants used for state flags */

    /** flag indicating that a slot in the hashtable is available */
    protected static final byte FREE = 0;

    /** flag indicating that a slot in the hashtable is occupied */
    protected static final byte FULL = 1;

    /** flag indicating that the value of a slot in the hashtable 
     * was deleted */
    protected static final byte REMOVED = 2;

    /**
     * Creates a new <code>THash</code> instance with the default
     * capacity and load factor.
     */
    public TPrimitiveHash() {
        super();
    }

    /**
     * Creates a new <code>TPrimitiveHash</code> instance with a prime
     * capacity at or near the specified capacity and with the default
     * load factor.
     *
     * @param initialCapacity an <code>int</code> value
     */
    public TPrimitiveHash(int initialCapacity) {
        this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }

    /**
     * Creates a new <code>TPrimitiveHash</code> instance with a prime
     * capacity at or near the minimum needed to hold
     * <tt>initialCapacity<tt> elements with load factor
     * <tt>loadFactor</tt> without triggering a rehash.
     *
     * @param initialCapacity an <code>int</code> value
     * @param loadFactor a <code>float</code> value
     */
    public TPrimitiveHash(int initialCapacity, float loadFactor) {
        super();
        _loadFactor = loadFactor;
        setUp((int)Math.ceil(initialCapacity / loadFactor));
    }

    public Object clone() {
        TPrimitiveHash h = (TPrimitiveHash)super.clone();
        h._states = (byte[])this._states.clone();
        return h;
    }

    /**
     * Returns the capacity of the hash table.  This is the true
     * physical capacity, without adjusting for the load factor.
     *
     * @return the physical capacity of the hash table.
     */
    protected int capacity() {
        return _states.length;
    }

    /**
     * Delete the record at <tt>index</tt>.
     *
     * @param index an <code>int</code> value
     */
    protected void removeAt(int index) {
        super.removeAt(index);
        _states[index] = REMOVED;
    }

    /**
     * initializes the hashtable to a prime capacity which is at least
     * <tt>initialCapacity + 1</tt>.  
     *
     * @param initialCapacity an <code>int</code> value
     * @return the actual capacity chosen
     */
    protected int setUp(int initialCapacity) {
        int capacity;

        capacity = super.setUp(initialCapacity);
        _states = new byte[capacity];
        return capacity;
    }
} // TPrimitiveHash