Class Hashing

java.lang.Object
com.google.common.hash.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 Summary

    Modifier and Type
    Method
    Description
    static HashFunction
    adler32()
    Returns a hash function implementing the Adler-32 checksum algorithm (32 hash bits) by delegating to the Adler32 Checksum.
    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.
    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.
    static HashFunction
    concatenating(HashFunction first, HashFunction second, HashFunction... rest)
    Returns a hash function which computes its hash code by concatenating the hash codes of the underlying hash functions together.
    static HashFunction
    concatenating(Iterable<HashFunction> hashFunctions)
    Returns a hash function which computes its hash code by concatenating the hash codes of the underlying hash functions together.
    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.
    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.
    static HashFunction
    crc32()
    Returns a hash function implementing the CRC-32 checksum algorithm (32 hash bits) by delegating to the CRC32 Checksum.
    static HashFunction
    crc32c()
    Returns a hash function implementing the CRC32C checksum algorithm (32 hash bits) as described by RFC 3720, Section 12.1.
    static HashFunction
    farmHashFingerprint64()
    Returns a hash function implementing FarmHash's Fingerprint64, an open-source algorithm.
    static HashFunction
    goodFastHash(int minimumBits)
    Returns a general-purpose, temporary-use, non-cryptographic hash function.
    static HashFunction
    hmacMd5(byte[] key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and a
    invalid reference 
    SecretSpecKey
    created from the given byte array and the MD5 algorithm.
    static HashFunction
    hmacMd5(Key key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and the given secret key.
    static HashFunction
    hmacSha1(byte[] key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and a
    invalid reference 
    SecretSpecKey
    created from the given byte array and the SHA-1 algorithm.
    static HashFunction
    hmacSha1(Key key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and the given secret key.
    static HashFunction
    hmacSha256(byte[] key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and a
    invalid reference 
    SecretSpecKey
    created from the given byte array and the SHA-256 algorithm.
    static HashFunction
    hmacSha256(Key key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and the given secret key.
    static HashFunction
    hmacSha512(byte[] key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and a
    invalid reference 
    SecretSpecKey
    created from the given byte array and the SHA-512 algorithm.
    static HashFunction
    hmacSha512(Key key)
    Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and the given secret key.
    static HashFunction
    md5()
    Returns a hash function implementing the MD5 hash algorithm (128 hash bits) by delegating to the MD5 MessageDigest.
    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.
    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.
    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.
    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.
    static HashFunction
    sha1()
    Returns a hash function implementing the SHA-1 algorithm (160 hash bits) by delegating to the SHA-1 MessageDigest.
    static HashFunction
    sha256()
    Returns a hash function implementing the SHA-256 algorithm (256 hash bits) by delegating to the SHA-256 MessageDigest.
    static HashFunction
    sha384()
    Returns a hash function implementing the SHA-384 algorithm (384 hash bits) by delegating to the SHA-384 MessageDigest.
    static HashFunction
    sha512()
    Returns a hash function implementing the SHA-512 algorithm (512 hash bits) by delegating to the SHA-512 MessageDigest.
    static HashFunction
    sipHash24()
    Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using a seed value of k = 00 01 02 ....
    static HashFunction
    sipHash24(long k0, long k1)
    Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using the given seed.

    Methods inherited from class Object

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

  • Method Details

    • 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).

    • sipHash24

      public static HashFunction sipHash24()
      Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using a seed value of k = 00 01 02 ....
      Since:
      15.0

    • sipHash24

      public static HashFunction sipHash24(long k0, long k1)
      Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using the given seed.
      Since:
      15.0

    • md5

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

      Warning: MD5 is not cryptographically secure or collision-resistant and is not recommended for use in new code. It should be used for legacy compatibility reasons only. Please consider using a hash function in the SHA-2 family of functions (e.g., SHA-256).

    • sha1

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

      Warning: SHA1 is not cryptographically secure and is not recommended for use in new code. It should be used for legacy compatibility reasons only. Please consider using a hash function in the SHA-2 family of functions (e.g., SHA-256).

    • sha256

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

    • sha384

      public static HashFunction sha384()
      Returns a hash function implementing the SHA-384 algorithm (384 hash bits) by delegating to the SHA-384 MessageDigest.
      Since:
      19.0

    • sha512

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

    • hmacMd5

      public static HashFunction hmacMd5(Key key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and the given secret key.
      Parameters:
      key - the secret key
      Throws:
      IllegalArgumentException - if the given key is inappropriate for initializing this MAC
      Since:
      20.0

    • hmacMd5

      public static HashFunction hmacMd5(byte[] key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and a
      invalid reference 
      SecretSpecKey
      created from the given byte array and the MD5 algorithm.
      Parameters:
      key - the key material of the secret key
      Since:
      20.0

    • hmacSha1

      public static HashFunction hmacSha1(Key key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and the given secret key.
      Parameters:
      key - the secret key
      Throws:
      IllegalArgumentException - if the given key is inappropriate for initializing this MAC
      Since:
      20.0

    • hmacSha1

      public static HashFunction hmacSha1(byte[] key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and a
      invalid reference 
      SecretSpecKey
      created from the given byte array and the SHA-1 algorithm.
      Parameters:
      key - the key material of the secret key
      Since:
      20.0

    • hmacSha256

      public static HashFunction hmacSha256(Key key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and the given secret key.
      Parameters:
      key - the secret key
      Throws:
      IllegalArgumentException - if the given key is inappropriate for initializing this MAC
      Since:
      20.0

    • hmacSha256

      public static HashFunction hmacSha256(byte[] key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and a
      invalid reference 
      SecretSpecKey
      created from the given byte array and the SHA-256 algorithm.
      Parameters:
      key - the key material of the secret key
      Since:
      20.0

    • hmacSha512

      public static HashFunction hmacSha512(Key key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and the given secret key.
      Parameters:
      key - the secret key
      Throws:
      IllegalArgumentException - if the given key is inappropriate for initializing this MAC
      Since:
      20.0

    • hmacSha512

      public static HashFunction hmacSha512(byte[] key)
      Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and a
      invalid reference 
      SecretSpecKey
      created from the given byte array and the SHA-512 algorithm.
      Parameters:
      key - the key material of the secret key
      Since:
      20.0

    • crc32c

      public static HashFunction crc32c()
      Returns a hash function implementing the CRC32C checksum algorithm (32 hash bits) as described by RFC 3720, Section 12.1.
      Since:
      18.0

    • crc32

      public static HashFunction crc32()
      Returns a hash function implementing the CRC-32 checksum algorithm (32 hash bits) by delegating to the CRC32 Checksum.

      To get the long value equivalent to Checksum.getValue() for a HashCode produced by this function, use HashCode.padToLong().

      Since:
      14.0

    • adler32

      public static HashFunction adler32()
      Returns a hash function implementing the Adler-32 checksum algorithm (32 hash bits) by delegating to the Adler32 Checksum.

      To get the long value equivalent to Checksum.getValue() for a HashCode produced by this function, use HashCode.padToLong().

      Since:
      14.0

    • farmHashFingerprint64

      public static HashFunction farmHashFingerprint64()
      Returns a hash function implementing FarmHash's Fingerprint64, an open-source algorithm.

      This is designed for generating persistent fingerprints of strings. It isn't cryptographically secure, but it produces a high-quality hash with fewer collisions than some alternatives we've used in the past. FarmHashFingerprints generated using this are byte-wise identical to those created using the C++ version, but note that this uses unsigned integers (see UnsignedInts). Comparisons between the two should take this into account.

      Since:
      20.0

    • 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)

      This method is suitable for the common use case of dividing work among buckets that meet the following conditions:

      • You want to assign the same fraction of inputs to each bucket.
      • When you reduce the number of buckets, you can accept that the most recently added buckets will be removed first. More concretely, if you are dividing traffic among tasks, you can decrease the number of tasks from 15 and 10, killing off the final 5 tasks, and consistentHash will handle it. If, however, you are dividing traffic among servers alpha, bravo, and charlie and you occasionally need to take each of the servers offline, consistentHash will be a poor fit: It provides no way for you to specify which of the three buckets is disappearing. Thus, if your buckets change from [alpha, bravo, charlie] to [bravo, charlie], it will assign all the old alpha traffic to bravo and all the old bravo traffic to charlie, rather than letting bravo keep its traffic.

      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)

      This method is suitable for the common use case of dividing work among buckets that meet the following conditions:

      • You want to assign the same fraction of inputs to each bucket.
      • When you reduce the number of buckets, you can accept that the most recently added buckets will be removed first. More concretely, if you are dividing traffic among tasks, you can decrease the number of tasks from 15 and 10, killing off the final 5 tasks, and consistentHash will handle it. If, however, you are dividing traffic among servers alpha, bravo, and charlie and you occasionally need to take each of the servers offline, consistentHash will be a poor fit: It provides no way for you to specify which of the three buckets is disappearing. Thus, if your buckets change from [alpha, bravo, charlie] to [bravo, charlie], it will assign all the old alpha traffic to bravo and all the old bravo traffic to charlie, rather than letting bravo keep its traffic.

      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

    • concatenating

      public static HashFunction concatenating(HashFunction first, HashFunction second, HashFunction... rest)
      Returns a hash function which computes its hash code by concatenating the hash codes of the underlying hash functions together. This can be useful if you need to generate hash codes of a specific length.

      For example, if you need 1024-bit hash codes, you could join two sha512() hash functions together: Hashing.concatenating(Hashing.sha512(), Hashing.sha512()).

      Since:
      19.0

    • concatenating

      public static HashFunction concatenating(Iterable<HashFunction> hashFunctions)
      Returns a hash function which computes its hash code by concatenating the hash codes of the underlying hash functions together. This can be useful if you need to generate hash codes of a specific length.

      For example, if you need 1024-bit hash codes, you could join two sha512() hash functions together: Hashing.concatenating(Hashing.sha512(), Hashing.sha512()).

      Since:
      19.0