Package com.google.common.hash

Class Hashing

  • @Beta
public final class Hashing
extends Object
    Static methods to obtain HashFunction instances, and other static hashing-related utilities.

    A comparison of the various hash functions can be found here.

    Since:
    11.0

    • Method Detail

      • goodFastHash

        public static HashFunction goodFastHash​(int minimumBits)
        Returns a general-purpose, temporary-use, non-cryptographic hash function. The algorithm the returned function implements is unspecified and subject to change without notice.

        Warning: a new random seed for these functions is chosen each time the Hashing class is loaded. Do not use this method if hash codes may escape the current process in any way, for example being sent over RPC, or saved to disk.

        Repeated calls to this method on the same loaded Hashing class, using the same value for minimumBits, will return identically-behaving HashFunction instances.

        Parameters:
        minimumBits - a positive integer (can be arbitrarily large)
        Returns:
        a hash function, described above, that produces hash codes of length minimumBits or greater

      • murmur3_32

        public static HashFunction murmur3_32​(int seed)
        Returns a hash function implementing the 32-bit murmur3 algorithm, x86 variant (little-endian variant), using the given seed value.

        The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A).

      • murmur3_32

        public static HashFunction murmur3_32()
        Returns a hash function implementing the 32-bit murmur3 algorithm, x86 variant (little-endian variant), using a seed value of zero.

        The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A).

      • murmur3_128

        public static HashFunction murmur3_128​(int seed)
        Returns a hash function implementing the 128-bit murmur3 algorithm, x64 variant (little-endian variant), using the given seed value.

        The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F).

      • murmur3_128

        public static HashFunction murmur3_128()
        Returns a hash function implementing the 128-bit murmur3 algorithm, x64 variant (little-endian variant), using a seed value of zero.

        The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F).

      • md5

        public static HashFunction md5()
        Returns a hash function implementing the MD5 hash algorithm (128 hash bits) by delegating to the MD5 MessageDigest.

      • sha1

        public static HashFunction sha1()
        Returns a hash function implementing the SHA-1 algorithm (160 hash bits) by delegating to the SHA-1 MessageDigest.

      • sha256

        public static HashFunction sha256()
        Returns a hash function implementing the SHA-256 algorithm (256 hash bits) by delegating to the SHA-256 MessageDigest.

      • sha512

        public static HashFunction sha512()
        Returns a hash function implementing the SHA-512 algorithm (512 hash bits) by delegating to the SHA-512 MessageDigest.

      • consistentHash

        public static int consistentHash​(HashCode hashCode,
                                 int buckets)
        Assigns to hashCode a "bucket" in the range [0, buckets), in a uniform manner that minimizes the need for remapping as buckets grows. That is, consistentHash(h, n) equals:
        • n - 1, with approximate probability 1/n
        • consistentHash(h, n - 1), otherwise (probability 1 - 1/n)

        See the wikipedia article on consistent hashing for more information.

      • consistentHash

        public static int consistentHash​(long input,
                                 int buckets)
        Assigns to input a "bucket" in the range [0, buckets), in a uniform manner that minimizes the need for remapping as buckets grows. That is, consistentHash(h, n) equals:
        • n - 1, with approximate probability 1/n
        • consistentHash(h, n - 1), otherwise (probability 1 - 1/n)

        See the wikipedia article on consistent hashing for more information.

      • combineOrdered

        public static HashCode combineOrdered​(Iterable<HashCode> hashCodes)
        Returns a hash code, having the same bit length as each of the input hash codes, that combines the information of these hash codes in an ordered fashion. That is, whenever two equal hash codes are produced by two calls to this method, it is as likely as possible that each was computed from the same input hash codes in the same order.
        Throws:
        IllegalArgumentException - if hashCodes is empty, or the hash codes do not all have the same bit length

      • combineUnordered

        public static HashCode combineUnordered​(Iterable<HashCode> hashCodes)
        Returns a hash code, having the same bit length as each of the input hash codes, that combines the information of these hash codes in an unordered fashion. That is, whenever two equal hash codes are produced by two calls to this method, it is as likely as possible that each was computed from the same input hash codes in some order.
        Throws:
        IllegalArgumentException - if hashCodes is empty, or the hash codes do not all have the same bit length