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Java > Open Source Codes > org > archive > util > BloomFilter


1 /* BloomFilter
2 *
3 * $Id: BloomFilter.java,v 1.2 2005/07/05 19:20:03 gojomo Exp $
4 *
5 * Created on Jun 30, 2005
6 *
7 * Copyright (C) 2005 Internet Archive; an adaptation of
8 * LGPL work (C) Sebastiano Vigna
9 *
10 * This file is part of the Heritrix web crawler (crawler.archive.org).
11 *
12 * Heritrix is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Lesser Public License as published by
14 * the Free Software Foundation; either version 2.1 of the License, or
15 * any later version.
16 *
17 * Heritrix is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Lesser Public License for more details.
21 *
22 * You should have received a copy of the GNU Lesser Public License
23 * along with Heritrix; if not, write to the Free Software
24 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25 */
26
27 package org.archive.util;
28
29 /**
30  * Common interface for different Bloom filter
31  * implementations
32  *
33  * @author Gordon Mohr
34  */
35 public interface BloomFilter {
36     /** The number of character sequences in the filter.
37      *
38      * @return the number of character sequences in the filter (but see {@link #contains(CharSequence)}).
39      */
40     public abstract int size();
41
42     /** Checks whether the given character sequence is in this filter.
43      *
44      * <P>Note that this method may return true on a character sequence that is has
45      * not been added to the filter. This will happen with probability 2<sub>-<var>d</var></sub>,
46      * where <var>d</var> is the number of hash functions specified at creation time, if
47      * the number of the elements in the filter is less than <var>n</var>, the number
48      * of expected elements specified at creation time.
49      *
50      * @param s a character sequence.
51      * @return true if the sequence is in the filter (or if a sequence with the
52      * same hash sequence is in the filter).
53      */
54     public abstract boolean contains(final CharSequence JavaDoc s);
55
56     /** Adds a character sequence to the filter.
57      *
58      * @param s a character sequence.
59      * @return true if the character sequence was not in the filter (but see {@link #contains(CharSequence)}).
60      */
61     public abstract boolean add(final CharSequence JavaDoc s);
62
63     /**
64      * The amount of memory in bytes consumed by the bloom
65      * bitfield.
66      *
67      * @return memory used by bloom bitfield, in bytes
68      */
69     public abstract long getSizeBytes();
70 }
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