Class BloomFilter<T>
 All Implemented Interfaces:
Size64
,Serializable
Instances of this class represent a set of elements (with false positives) using a Bloom filter (Burton H. Bloom, “Space/time tradeoffs in hash coding with allowable errors”, Comm. ACM 13(7):422−426, 1970). Because of the way Bloom filters work, you cannot remove elements.
Given a maximum number of elements, Bloom filters have an expected error rate that depends on the number of hash functions used. More precisely, a Bloom filter for at most n elements with d hash functions will use ln 2 dn ≈ 1.44 dn bits; false positives will happen with probability 2^{d}. Adding more than n elements will result in a higher rate of false positives. You can conveniently build a filter by specifying the number of hash function, by specifying the expected false positive rate, or just requesting essentially no false positives.
The maximum number of bits supported is 137438953408L, which makes it possible to store with high precision several dozens billion elements.
This class exports access methods that are similar to those of Set
, but it
does not implement that interface, as too many nonoptional methods would be unimplementable
(e.g., iterators). To store generic objects of type T
, we rely on MurmurHash3
and Google Guava's funnels, which are strategies turning an object into a sequence of bytes.
There are predefined methods for storing character sequences,
byte and character arrays,
integers and longs; they use the readymade funnels available in Funnels
.
You can define your own Funnel
and store objects correspondingly.
If you intend to storage sequences of bytes which are already random looking (e.g., MD5 digests) you can
use the addHash(byte[])
/containsHash(byte[])
methods, which use the first 16 bytes
of the argument byte array directly, without further hashing.
If you plan to use predefined methods only, the suggested way to instantiate this class is to use the
factory methods without Funnel
arguments (e.g., create(long, int)
). They
return a filter of generic type Void
using a null
funnel
that will be never invoked (unless you circument the generics typesafety mechanisms).
A main method makes it easy to create serialized Bloom filters starting from a list of strings.
Implementation details
To generate several hash functions we use the technique suggested by Adam Kirsch and Michael Mitzenmacher in “Less hashing,
same performance: Building a better Bloom filter”, Random Structures &
Algorithms, 33(2):187−218, John Wiley & Sons, 2008. Two 64bit hashes h_{0} and
h_{1} are generated using Hashing.murmur3_128()
(or taken from the argument,
in case of addHash(byte[])
/containsHash(byte[])
). Then, the hash
function of index i is simply h_{0} + ih_{1} (i ≥ 0). The
paper proves that this choice does not worsen the rate of false positives.
 Author:
 Sebastiano Vigna
 See Also:

Field Summary
Modifier and TypeFieldDescriptionstatic final com.google.common.hash.Funnel<byte[]>
Funnels.byteArrayFunnel()
.static final com.google.common.hash.Funnel<Integer>
Funnels.integerFunnel()
.static final com.google.common.hash.Funnel<Long>
Funnels.longFunnel()
.static final long
The maximum number of bits in a filter (limited by array size and bits in a long).static final com.google.common.hash.Funnel<CharSequence>
Funnels.unencodedCharsFunnel()
. 
Constructor Summary
ModifierConstructorDescriptionprotected
BloomFilter
(long n, int d, com.google.common.hash.Funnel<T> funnel) Creates a new Bloom filter with given number of hash functions and expected number of elements of given type. 
Method Summary
Modifier and TypeMethodDescriptionboolean
add
(byte[] a) Adds a byte array to this filter.boolean
add
(char[] a) Adds a character array to this filter.boolean
add
(int x) Adds an integer to this filter.boolean
add
(long x) Adds a long to this filter.boolean
add
(CharSequence s) Adds a character sequence to this filter.boolean
Adds an object of generic type to this filter using the funnel specified at construction time.<V> boolean
add
(V e, com.google.common.hash.Funnel<V> funnel) Adds an object to this filter using a specified funnel.boolean
addHash
(byte[] hash) Adds a hash code to this filter.void
clear()
Clears this filter.boolean
contains
(byte[] a) Checks whether the given byte array is in this filter.boolean
contains
(char[] a) Checks whether the given character array is in this filter.boolean
contains
(int x) Adds an integer is in this filter.boolean
contains
(long x) Checks whether the given long is in this filter.boolean
Checks whether the given character sequence is in this filter.boolean
Checks whether an object of generic type is in this filter using the funnel specified at construction time.boolean
containsHash
(byte[] hash) Checks whether a hash code is in this filter.static BloomFilter<Void>
create
(long n) Creates a new highprecision Bloom filter a given expected number of elements.static BloomFilter<Void>
create
(long n, double precision) Creates a new Bloom filter onVoid
with given precision and expected number of elements.static <T> BloomFilter<T>
create
(long n, double precision, com.google.common.hash.Funnel<T> funnel) Creates a new Bloom filter onVoid
with given precision and expected number of elements of given type.static BloomFilter<Void>
create
(long n, int d) Creates a new Bloom filter with given number of hash functions and expected number of elements.static <T> BloomFilter<T>
create
(long n, int d, com.google.common.hash.Funnel<T> funnel) Creates a new Bloom filter with given number of hash functions and expected number of elements of given type.static <T> BloomFilter<T>
create
(long n, com.google.common.hash.Funnel<T> funnel) Creates a new highprecision Bloom filter a given expected number of elements of given type.static void
int
size()
Deprecated.long
size64()
Returns the size of this filter.

Field Details

BYTE_ARRAY_FUNNEL
public static final com.google.common.hash.Funnel<byte[]> BYTE_ARRAY_FUNNELFunnels.byteArrayFunnel()
. 
STRING_FUNNEL
Funnels.unencodedCharsFunnel()
. 
INTEGER_FUNNEL
Funnels.integerFunnel()
. 
LONG_FUNNEL
Funnels.longFunnel()
. 
MAX_BITS
public static final long MAX_BITSThe maximum number of bits in a filter (limited by array size and bits in a long). See Also:


Constructor Details

BloomFilter
Creates a new Bloom filter with given number of hash functions and expected number of elements of given type. Parameters:
n
 the expected number of elements.d
 the number of hash functions; if no more thann
elements are added to this filter, false positives will happen with probability 2^{d}.funnel
 a funnel for the elements of this filter.


Method Details

create
Creates a new highprecision Bloom filter a given expected number of elements of given type.This constructor uses a number of hash functions that is logarithmic in the number of expected elements. This usually results in no false positives at all.
 Parameters:
n
 the expected number of elements.funnel
 a funnel for the elements of this filter (usecreate(long)
if you plan on using only the predefined methods).

create
Creates a new Bloom filter with given number of hash functions and expected number of elements of given type. Parameters:
n
 the expected number of elements.d
 the number of hash functions; if no more thann
elements are added to this filter, false positives will happen with probability 2^{d}.funnel
 a funnel for the elements of this filter (usecreate(long, int)
if you plan on using only the predefined methods).

create
public static <T> BloomFilter<T> create(long n, double precision, com.google.common.hash.Funnel<T> funnel) Creates a new Bloom filter onVoid
with given precision and expected number of elements of given type. Parameters:
n
 the expected number of elements.precision
 the expected fraction of false positives; if no more thann
elements are added to this filter, false positives will happen with no more than this probability. plan on using only the predefined methods).funnel
 a funnel for the elements of this filter (usecreate(long, double)
if you plan on using only the predefined methods).

create
Creates a new highprecision Bloom filter a given expected number of elements.Filters created using this method will be accessible using predefined methods only. Use
create(long, Funnel)
if you need a generic filter.This constructor uses a number of hash functions that is logarithmic in the number of expected elements. This usually results in no false positives at all.
 Parameters:
n
 the expected number of elements.

create
Creates a new Bloom filter with given number of hash functions and expected number of elements.Filters created using this method will be accessible using predefined methods only. Use
create(long, int, Funnel)
if you need a generic filter. Parameters:
n
 the expected number of elements.d
 the number of hash functions; if no more thann
elements are added to this filter, false positives will happen with probability 2^{d}.

create
Creates a new Bloom filter onVoid
with given precision and expected number of elements.Filters created using this method will be accessible using predefined methods only. Use
create(long, double, Funnel)
if you need a generic filter. Parameters:
n
 the expected number of elements.precision
 the expected fraction of false positives; if no more thann
elements are added to this filter, false positives will happen with no more than this probability. plan on using only the predefined methods). See Also:

add
Adds a character sequence to this filter. Parameters:
s
 a character sequence. Returns:
 true if this filter was modified.

add
public boolean add(byte[] a) Adds a byte array to this filter. Parameters:
a
 a byte array. Returns:
 true if this filter was modified.

add
public boolean add(char[] a) Adds a character array to this filter. Parameters:
a
 a character array. Returns:
 true if this filter was modified.

add
public boolean add(int x) Adds an integer to this filter. Parameters:
x
 an integer. Returns:
 true if this filter was modified.

add
public boolean add(long x) Adds a long to this filter. Parameters:
x
 a long. Returns:
 true if this filter was modified.

add
Adds an object of generic type to this filter using the funnel specified at construction time. Parameters:
e
 an object. Returns:
 true if this filter was modified.

add
public <V> boolean add(V e, com.google.common.hash.Funnel<V> funnel) Adds an object to this filter using a specified funnel. Parameters:
e
 an object.funnel
 a funnel forobject
. Returns:
 true if this filter was modified.

addHash
public boolean addHash(byte[] hash) Adds a hash code to this filter.This method uses the first 16 bytes of a byte array to build two 64bit hashes. The intended usage is storing digests and similar alreadyhashed values.
 Parameters:
hash
 a byte array of at least 16 elements containing a hash code. Returns:
 true if this filter was modified.
 Throws:
ArrayIndexOutOfBoundsException
 ifhash
is shorter than 16. See Also:

contains
Checks whether the given character sequence is in this filter.Note that this method may return true on a character sequence that has never been added to this filter. This will happen with probability 2^{d}, where d is the number of hash functions specified at creation time, if the number of the elements in this filter is less than n, the number of expected elements specified at creation time.
 Parameters:
s
 a character sequence. Returns:
 true if
s
is in this filter.

contains
public boolean contains(byte[] a) Checks whether the given byte array is in this filter. Parameters:
a
 a byte array. Returns:
 true if
a
is in this filter.  See Also:

contains
public boolean contains(char[] a) Checks whether the given character array is in this filter. Parameters:
a
 a character array. Returns:
 true if
a
is in this filter.  See Also:

contains
public boolean contains(int x) Adds an integer is in this filter. Parameters:
x
 an integer. Returns:
 true if
x
is in this filter.  See Also:

contains
public boolean contains(long x) Checks whether the given long is in this filter. Parameters:
x
 a long. Returns:
 true if
x
is in this filter.  See Also:

contains
Checks whether an object of generic type is in this filter using the funnel specified at construction time. Parameters:
e
 an element. Returns:
 true if
e
is in this filter.  See Also:

containsHash
public boolean containsHash(byte[] hash) Checks whether a hash code is in this filter.This method uses the first 16 bytes of a byte array to build two 64bit hashes. The intended usage is storing digests and similar alreadyhashed values.
 Parameters:
hash
 a byte array of at least 16 elements containing a hash code. Returns:
 true if
hash
is in this filter.  Throws:
ArrayIndexOutOfBoundsException
 ifhash
is shorter than 16. See Also:

clear
public void clear()Clears this filter. 
size64
public long size64()Returns the size of this filter.Note that the size of a Bloom filter is only a lower bound for the number of distinct elements that have been added to this filter. False positives might make the number returned by this method smaller than it should be.

size
Deprecated. 
main
