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The Trove library provides high speed regular and primitive collections for Java.
There is a newer version: 3.0.3
///////////////////////////////////////////////////////////////////////////////
// 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;

import java.util.ConcurrentModificationException;
import java.util.NoSuchElementException;

/**
 * Abstract iterator class for THash implementations.  This class provides some
 * of the common iterator operations (hasNext(), remove()) and allows subclasses
 * to define the mechanism(s) for advancing the iterator and returning data.
 *
 * @author Eric D. Friedman
 * @version $Id: TIterator.java,v 1.3 2007/06/29 20:03:10 robeden Exp $
 */
abstract class TIterator {
    /** the data structure this iterator traverses */
    protected final THash _hash;
    /** the number of elements this iterator believes are in the
     * data structure it accesses. */
    protected int _expectedSize;
    /** the index used for iteration. */
    protected int _index;

    /**
     *  Create an instance of TIterator over the specified THash.
     */
    public TIterator(THash hash) {
        _hash = hash;
        _expectedSize = _hash.size();
        _index = _hash.capacity();
    }

    /**
     * Returns true if the iterator can be advanced past its current
     * location.
     *
     * @return a boolean value
     */
    public boolean hasNext() {
        return nextIndex() >= 0;
    }

    /**
     * Removes the last entry returned by the iterator.
     * Invoking this method more than once for a single entry
     * will leave the underlying data structure in a confused
     * state.
     */
    public void remove() {
        if (_expectedSize != _hash.size()) {
            throw new ConcurrentModificationException();
        }

        // Disable auto compaction during the remove. This is a workaround for bug 1642768.
        try {
            _hash.tempDisableAutoCompaction();
            _hash.removeAt(_index);
        }
        finally {
            _hash.reenableAutoCompaction( false );
        }

        _expectedSize--;
    }

    /**
     * Sets the internal index so that the `next' object
     * can be returned.
     */
    protected final void moveToNextIndex() {
        // doing the assignment && < 0 in one line shaves
        // 3 opcodes...
        if ((_index = nextIndex()) < 0) {
            throw new NoSuchElementException();
        }
    }

    /**
     * Returns the index of the next value in the data structure
     * or a negative value if the iterator is exhausted.
     *
     * @return an int value
     */
    abstract protected int nextIndex();
} // TIterator