Create a Dynamic Long Array in Java

/*from  w  w  w  .  jav  a2 s. c o  m*/
/*
Copyright (C) 2007  Mobixess Inc. http://www.java-objects-database.com

This file is part of the JODB (Java Objects Database) open source project.

JODB is free software; you can redistribute it and/or modify it under
the terms of version 2 of the GNU General Public License as published
by the Free Software Foundation.

JODB 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 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. 
*/

public class DynamicLongArray {
    final static int DEFAULT_CHUNK_SIZE = 256;
    final static int DEFAULT_CHUNKS = 16;

    private int _chunkSize;
    private long[][] _data;
    private int _length;


    public DynamicLongArray() {
        this(DEFAULT_CHUNK_SIZE);
    }

    public DynamicLongArray(int chunkSize) {
        _chunkSize = chunkSize;
        _data = new long[DEFAULT_CHUNKS][];
    }

    public boolean isEmpty() {
        return (_length == 0);
    }

    private void ensureCapacity(int index) {
        if (index >= _length) {
            int i = index / _chunkSize;
            if (i >= _data.length) {
                // grow by 50%
                int new_size = (i * 3) / 2 + 1;
                long[][] newChunk = new long[new_size][];
                System.arraycopy(_data, 0, newChunk, 0, _data.length);
                _data = newChunk;
            }
            _length = index + 1;
        }
    }

    public long get(int index) {
        if (index >= _length) {
            throw new IndexOutOfBoundsException("Index " + index
                    + " is outside of 0.." + (_length - 1));
        }
        int i = index / _chunkSize;
        int j = index % _chunkSize;
        if (_data[i] == null) {
            return 0;
        } else {
            return _data[i][j];
        }
    }

    public void set(int index, long value) {
        int i = index / _chunkSize;
        int j = index % _chunkSize;
        ensureCapacity(index);
        if (_data[i] == null) {
            _data[i] = new long[_chunkSize];
        }
        _data[i][j] = value;
    }

    public int size() {
        return _length;
    }

    public String toString() {
        int i;
        StringBuffer sb = new StringBuffer(_length * 4);
        sb.append('{');
        int l = _length - 1;
        for (i = 0; i < l; i++) {
            sb.append(get(i));
            sb.append(',');
        }
        sb.append(get(i));
        sb.append('}');
        return sb.toString();
    }
}