Package com.google.common.hash

Class BloomFilter<T>

  • Type Parameters:
    T - the type of instances that the BloomFilter accepts
    All Implemented Interfaces:
    Predicate<T>, java.io.Serializable, java.util.function.Predicate<T>
    @Beta
public final class BloomFilter<T>
extends java.lang.Object
implements Predicate<T>, java.io.Serializable
    A Bloom filter for instances of T. A Bloom filter offers an approximate containment test with one-sided error: if it claims that an element is contained in it, this might be in error, but if it claims that an element is not contained in it, then this is definitely true.

    If you are unfamiliar with Bloom filters, this nice tutorial may help you understand how they work.

    The false positive probability (FPP) of a Bloom filter is defined as the probability that mightContain(Object) will erroneously return true for an object that has not actually been put in the BloomFilter.

    Bloom filters are serializable. They also support a more compact serial representation via the writeTo(java.io.OutputStream) and readFrom(java.io.InputStream, com.google.common.hash.Funnel<? super T>) methods. Both serialized forms will continue to be supported by future versions of this library. However, serial forms generated by newer versions of the code may not be readable by older versions of the code (e.g., a serialized Bloom filter generated today may not be readable by a binary that was compiled 6 months ago).

    As of Guava 23.0, this class is thread-safe and lock-free. It internally uses atomics and compare-and-swap to ensure correctness when multiple threads are used to access it.

    Since:
    11.0 (thread-safe since 23.0)
    See Also:
    Serialized Form

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      private static class  BloomFilter.SerialForm<T>  
      (package private) static interface  BloomFilter.Strategy
      A strategy to translate T instances, to numHashFunctions bit indexes.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods 
      Modifier and Type Method Description
      boolean apply​(T input)
      Deprecated.
      Provided only to satisfy the Predicate interface; use mightContain(T) instead.
      long approximateElementCount()
      Returns an estimate for the total number of distinct elements that have been added to this Bloom filter.
      (package private) long bitSize()
      Returns the number of bits in the underlying bit array.
      BloomFilter<T> copy()
      Creates a new BloomFilter that's a copy of this instance.
      static <T> BloomFilter<T> create​(Funnel<? super T> funnel, int expectedInsertions)
      Creates a BloomFilter with the expected number of insertions and a default expected false positive probability of 3%.
      static <T> BloomFilter<T> create​(Funnel<? super T> funnel, int expectedInsertions, double fpp)
      Creates a BloomFilter with the expected number of insertions and expected false positive probability.
      static <T> BloomFilter<T> create​(Funnel<? super T> funnel, long expectedInsertions)
      Creates a BloomFilter with the expected number of insertions and a default expected false positive probability of 3%.
      static <T> BloomFilter<T> create​(Funnel<? super T> funnel, long expectedInsertions, double fpp)
      Creates a BloomFilter with the expected number of insertions and expected false positive probability.
      (package private) static <T> BloomFilter<T> create​(Funnel<? super T> funnel, long expectedInsertions, double fpp, BloomFilter.Strategy strategy)  
      boolean equals​(java.lang.Object object)
      Indicates whether another object is equal to this predicate.
      double expectedFpp()
      Returns the probability that mightContain(Object) will erroneously return true for an object that has not actually been put in the BloomFilter.
      int hashCode()  
      boolean isCompatible​(BloomFilter<T> that)
      Determines whether a given Bloom filter is compatible with this Bloom filter.
      boolean mightContain​(T object)
      Returns true if the element might have been put in this Bloom filter, false if this is definitely not the case.
      (package private) static long optimalNumOfBits​(long n, double p)
      Computes m (total bits of Bloom filter) which is expected to achieve, for the specified expected insertions, the required false positive probability.
      (package private) static int optimalNumOfHashFunctions​(long n, long m)
      Computes the optimal k (number of hashes per element inserted in Bloom filter), given the expected insertions and total number of bits in the Bloom filter.
      boolean put​(T object)
      Puts an element into this BloomFilter.
      void putAll​(BloomFilter<T> that)
      Combines this Bloom filter with another Bloom filter by performing a bitwise OR of the underlying data.
      static <T> BloomFilter<T> readFrom​(java.io.InputStream in, Funnel<? super T> funnel)
      Reads a byte stream, which was written by writeTo(OutputStream), into a BloomFilter.
      static <T> java.util.stream.Collector<T,​?,​BloomFilter<T>> toBloomFilter​(Funnel<? super T> funnel, long expectedInsertions)
      Returns a Collector expecting the specified number of insertions, and yielding a BloomFilter with false positive probability 3%.
      static <T> java.util.stream.Collector<T,​?,​BloomFilter<T>> toBloomFilter​(Funnel<? super T> funnel, long expectedInsertions, double fpp)
      Returns a Collector expecting the specified number of insertions, and yielding a BloomFilter with the specified expected false positive probability.
      private java.lang.Object writeReplace()  
      void writeTo​(java.io.OutputStream out)
      Writes this BloomFilter to an output stream, with a custom format (not Java serialization).

      • Methods inherited from class java.lang.Object

        clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

      • Methods inherited from interface com.google.common.base.Predicate

        test

      • Methods inherited from interface java.util.function.Predicate

        and, negate, or

    • Field Detail

      • numHashFunctions

        private final int numHashFunctions
        Number of hashes per element

      • funnel

        private final Funnel<? super T> funnel
        The funnel to translate Ts to bytes

      • strategy

        private final BloomFilter.Strategy strategy
        The strategy we employ to map an element T to numHashFunctions bit indexes.

    • Method Detail

      • copy

        public BloomFilter<T> copy()
        Creates a new BloomFilter that's a copy of this instance. The new instance is equal to this instance but shares no mutable state.
        Since:
        12.0

      • mightContain

        public boolean mightContain​(T object)
        Returns true if the element might have been put in this Bloom filter, false if this is definitely not the case.

      • apply

        @Deprecated
public boolean apply​(T input)
        Deprecated.
        Provided only to satisfy the Predicate interface; use mightContain(T) instead.
        Description copied from interface: Predicate
        Returns the result of applying this predicate to input (Java 8 users, see notes in the class documentation above). This method is generally expected, but not absolutely required, to have the following properties:
        • Its execution does not cause any observable side effects.
        • The computation is consistent with equals; that is, Objects.equal(a, b) implies that predicate.apply(a) == predicate.apply(b)).
        Specified by:
        apply in interface Predicate<T>

      • put

        public boolean put​(T object)
        Puts an element into this BloomFilter. Ensures that subsequent invocations of mightContain(Object) with the same element will always return true.
        Returns:
        true if the Bloom filter's bits changed as a result of this operation. If the bits changed, this is definitely the first time object has been added to the filter. If the bits haven't changed, this might be the first time object has been added to the filter. Note that put(t) always returns the opposite result to what mightContain(t) would have returned at the time it is called.
        Since:
        12.0 (present in 11.0 with void return type})

      • expectedFpp

        public double expectedFpp()
        Returns the probability that mightContain(Object) will erroneously return true for an object that has not actually been put in the BloomFilter.

        Ideally, this number should be close to the fpp parameter passed in create(Funnel, int, double), or smaller. If it is significantly higher, it is usually the case that too many elements (more than expected) have been put in the BloomFilter, degenerating it.

        Since:
        14.0 (since 11.0 as expectedFalsePositiveProbability())

      • approximateElementCount

        public long approximateElementCount()
        Returns an estimate for the total number of distinct elements that have been added to this Bloom filter. This approximation is reasonably accurate if it does not exceed the value of expectedInsertions that was used when constructing the filter.
        Since:
        22.0

      • bitSize

        long bitSize()
        Returns the number of bits in the underlying bit array.

      • isCompatible

        public boolean isCompatible​(BloomFilter<T> that)
        Determines whether a given Bloom filter is compatible with this Bloom filter. For two Bloom filters to be compatible, they must:
        • not be the same instance
        • have the same number of hash functions
        • have the same bit size
        • have the same strategy
        • have equal funnels
        Parameters:
        that - The Bloom filter to check for compatibility.
        Since:
        15.0

      • putAll

        public void putAll​(BloomFilter<T> that)
        Combines this Bloom filter with another Bloom filter by performing a bitwise OR of the underlying data. The mutations happen to this instance. Callers must ensure the Bloom filters are appropriately sized to avoid saturating them.
        Parameters:
        that - The Bloom filter to combine this Bloom filter with. It is not mutated.
        Throws:
        java.lang.IllegalArgumentException - if isCompatible(that) == false
        Since:
        15.0

      • equals

        public boolean equals​(java.lang.Object object)
        Description copied from interface: Predicate
        Indicates whether another object is equal to this predicate.

        Most implementations will have no reason to override the behavior of Object.equals(java.lang.Object). However, an implementation may also choose to return true whenever object is a Predicate that it considers interchangeable with this one. "Interchangeable" typically means that this.apply(t) == that.apply(t) for all t of type T). Note that a false result from this method does not imply that the predicates are known not to be interchangeable.

        Specified by:
        equals in interface Predicate<T>
        Overrides:
        equals in class java.lang.Object

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class java.lang.Object

      • toBloomFilter

        public static <T> java.util.stream.Collector<T,​?,​BloomFilter<T>> toBloomFilter​(Funnel<? super T> funnel,
                                                                                           long expectedInsertions)
        Returns a Collector expecting the specified number of insertions, and yielding a BloomFilter with false positive probability 3%.

        Note that if the Collector receives significantly more elements than specified, the resulting BloomFilter will suffer a sharp deterioration of its false positive probability.

        The constructed BloomFilter will be serializable if the provided Funnel<T> is.

        It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since equals(java.lang.Object) also relies on object identity of funnels.

        Parameters:
        funnel - the funnel of T's that the constructed BloomFilter will use
        expectedInsertions - the number of expected insertions to the constructed BloomFilter; must be positive
        Returns:
        a Collector generating a BloomFilter of the received elements
        Since:
        23.0

      • toBloomFilter

        public static <T> java.util.stream.Collector<T,​?,​BloomFilter<T>> toBloomFilter​(Funnel<? super T> funnel,
                                                                                           long expectedInsertions,
                                                                                           double fpp)
        Returns a Collector expecting the specified number of insertions, and yielding a BloomFilter with the specified expected false positive probability.

        Note that if the Collector receives significantly more elements than specified, the resulting BloomFilter will suffer a sharp deterioration of its false positive probability.

        The constructed BloomFilter will be serializable if the provided Funnel<T> is.

        It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since equals(java.lang.Object) also relies on object identity of funnels.

        Parameters:
        funnel - the funnel of T's that the constructed BloomFilter will use
        expectedInsertions - the number of expected insertions to the constructed BloomFilter; must be positive
        fpp - the desired false positive probability (must be positive and less than 1.0)
        Returns:
        a Collector generating a BloomFilter of the received elements
        Since:
        23.0

      • create

        public static <T> BloomFilter<T> create​(Funnel<? super T> funnel,
                                        int expectedInsertions,
                                        double fpp)
        Creates a BloomFilter with the expected number of insertions and expected false positive probability.

        Note that overflowing a BloomFilter with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.

        The constructed BloomFilter will be serializable if the provided Funnel<T> is.

        It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since equals(java.lang.Object) also relies on object identity of funnels.

        Parameters:
        funnel - the funnel of T's that the constructed BloomFilter will use
        expectedInsertions - the number of expected insertions to the constructed BloomFilter; must be positive
        fpp - the desired false positive probability (must be positive and less than 1.0)
        Returns:
        a BloomFilter

      • create

        public static <T> BloomFilter<T> create​(Funnel<? super T> funnel,
                                        long expectedInsertions,
                                        double fpp)
        Creates a BloomFilter with the expected number of insertions and expected false positive probability.

        Note that overflowing a BloomFilter with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.

        The constructed BloomFilter will be serializable if the provided Funnel<T> is.

        It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since equals(java.lang.Object) also relies on object identity of funnels.

        Parameters:
        funnel - the funnel of T's that the constructed BloomFilter will use
        expectedInsertions - the number of expected insertions to the constructed BloomFilter; must be positive
        fpp - the desired false positive probability (must be positive and less than 1.0)
        Returns:
        a BloomFilter
        Since:
        19.0

      • create

        public static <T> BloomFilter<T> create​(Funnel<? super T> funnel,
                                        int expectedInsertions)
        Creates a BloomFilter with the expected number of insertions and a default expected false positive probability of 3%.

        Note that overflowing a BloomFilter with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.

        The constructed BloomFilter will be serializable if the provided Funnel<T> is.

        It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since equals(java.lang.Object) also relies on object identity of funnels.

        Parameters:
        funnel - the funnel of T's that the constructed BloomFilter will use
        expectedInsertions - the number of expected insertions to the constructed BloomFilter; must be positive
        Returns:
        a BloomFilter

      • create

        public static <T> BloomFilter<T> create​(Funnel<? super T> funnel,
                                        long expectedInsertions)
        Creates a BloomFilter with the expected number of insertions and a default expected false positive probability of 3%.

        Note that overflowing a BloomFilter with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.

        The constructed BloomFilter will be serializable if the provided Funnel<T> is.

        It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since equals(java.lang.Object) also relies on object identity of funnels.

        Parameters:
        funnel - the funnel of T's that the constructed BloomFilter will use
        expectedInsertions - the number of expected insertions to the constructed BloomFilter; must be positive
        Returns:
        a BloomFilter
        Since:
        19.0

      • optimalNumOfHashFunctions

        static int optimalNumOfHashFunctions​(long n,
                                     long m)
        Computes the optimal k (number of hashes per element inserted in Bloom filter), given the expected insertions and total number of bits in the Bloom filter.

        See http://en.wikipedia.org/wiki/File:Bloom_filter_fp_probability.svg for the formula.

        Parameters:
        n - expected insertions (must be positive)
        m - total number of bits in Bloom filter (must be positive)

      • optimalNumOfBits

        static long optimalNumOfBits​(long n,
                             double p)
        Computes m (total bits of Bloom filter) which is expected to achieve, for the specified expected insertions, the required false positive probability.

        See http://en.wikipedia.org/wiki/Bloom_filter#Probability_of_false_positives for the formula.

        Parameters:
        n - expected insertions (must be positive)
        p - false positive rate (must be 0 < p < 1)

      • writeReplace

        private java.lang.Object writeReplace()

      • writeTo

        public void writeTo​(java.io.OutputStream out)
             throws java.io.IOException
        Writes this BloomFilter to an output stream, with a custom format (not Java serialization). This has been measured to save at least 400 bytes compared to regular serialization.

        Use readFrom(InputStream, Funnel) to reconstruct the written BloomFilter.

        Throws:
        java.io.IOException

      • readFrom

        public static <T> BloomFilter<T> readFrom​(java.io.InputStream in,
                                          Funnel<? super T> funnel)
                                   throws java.io.IOException
        Reads a byte stream, which was written by writeTo(OutputStream), into a BloomFilter.

        The Funnel to be used is not encoded in the stream, so it must be provided here. Warning: the funnel provided must behave identically to the one used to populate the original Bloom filter!

        Throws:
        java.io.IOException - if the InputStream throws an IOException, or if its data does not appear to be a BloomFilter serialized using the writeTo(OutputStream) method.