@Beta public final class Hashing extends Object
HashFunction
instances, and other static hashingrelated
utilities.
A comparison of the various hash functions can be found here.
Modifier and Type  Method and Description 

static HashFunction 
adler32()
Returns a hash function implementing the Adler32 checksum algorithm (32 hash bits).

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(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 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 HashFunction 
crc32()
Returns a hash function implementing the CRC32 checksum algorithm (32 hash bits).

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 opensource algorithm.

static HashFunction 
goodFastHash(int minimumBits)
Returns a generalpurpose, temporaryuse, noncryptographic 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
SecretKeySpec 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
SHA1 (160 hash bits) hash function and a
SecretKeySpec created from the given byte
array and the SHA1 algorithm. 
static HashFunction 
hmacSha1(Key key)
Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the
SHA1 (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
SHA256 (256 hash bits) hash function and a
SecretKeySpec created from the given byte
array and the SHA256 algorithm. 
static HashFunction 
hmacSha256(Key key)
Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the
SHA256 (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
SHA512 (512 hash bits) hash function and a
SecretKeySpec created from the given byte
array and the SHA512 algorithm. 
static HashFunction 
hmacSha512(Key key)
Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the
SHA512 (512 hash bits) hash function and the given secret key.

static HashFunction 
md5()
Deprecated.
If you must interoperate with a system that requires MD5, then use this method,
despite its deprecation. But if you can choose your hash function, avoid MD5, which is
neither fast nor secure. As of January 2017, we suggest:

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

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

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

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

static HashFunction 
sha1()
Deprecated.
If you must interoperate with a system that requires SHA1, then use this method,
despite its deprecation. But if you can choose your hash function, avoid SHA1, which is
neither fast nor secure. As of January 2017, we suggest:

static HashFunction 
sha256()
Returns a hash function implementing the SHA256 algorithm (256 hash bits).

static HashFunction 
sha384()
Returns a hash function implementing the SHA384 algorithm (384 hash bits).

static HashFunction 
sha512()
Returns a hash function implementing the SHA512 algorithm (512 hash bits).

static HashFunction 
sipHash24()
Returns a hash function implementing the 64bit
SipHash24 algorithm using a seed value of
k = 00 01 02 ... . 
static HashFunction 
sipHash24(long k0,
long k1)
Returns a hash function implementing the 64bit
SipHash24 algorithm using the given seed.

public static HashFunction goodFastHash(int minimumBits)
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. For a generalpurpose,
noncryptographic hash function that will never change behavior, we suggest murmur3_128(int)
.
Repeated calls to this method on the same loaded Hashing
class, using the same value
for minimumBits
, will return identicallybehaving HashFunction
instances.
minimumBits
 a positive integer (can be arbitrarily large)minimumBits
or greaterpublic static HashFunction murmur3_32(int seed)
The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A).
public static HashFunction murmur3_32()
The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A).
public static HashFunction murmur3_128(int seed)
The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F).
public static HashFunction murmur3_128()
The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F).
public static HashFunction sipHash24()
k = 00 01 02 ...
.public static HashFunction sipHash24(long k0, long k1)
@Deprecated public static HashFunction md5()
sha256()
or a higherlevel API.
goodFastHash(int)
, though see its docs for caveats.
@Deprecated public static HashFunction sha1()
sha256()
or a higherlevel API.
goodFastHash(int)
, though see its docs for caveats.
public static HashFunction sha256()
public static HashFunction sha384()
public static HashFunction sha512()
public static HashFunction hmacMd5(Key key)
key
 the secret keyIllegalArgumentException
 if the given key is inappropriate for initializing this MACpublic static HashFunction hmacMd5(byte[] key)
SecretKeySpec
created from the given byte array
and the MD5 algorithm.key
 the key material of the secret keypublic static HashFunction hmacSha1(Key key)
key
 the secret keyIllegalArgumentException
 if the given key is inappropriate for initializing this MACpublic static HashFunction hmacSha1(byte[] key)
SecretKeySpec
created from the given byte
array and the SHA1 algorithm.key
 the key material of the secret keypublic static HashFunction hmacSha256(Key key)
key
 the secret keyIllegalArgumentException
 if the given key is inappropriate for initializing this MACpublic static HashFunction hmacSha256(byte[] key)
SecretKeySpec
created from the given byte
array and the SHA256 algorithm.key
 the key material of the secret keypublic static HashFunction hmacSha512(Key key)
key
 the secret keyIllegalArgumentException
 if the given key is inappropriate for initializing this MACpublic static HashFunction hmacSha512(byte[] key)
SecretKeySpec
created from the given byte
array and the SHA512 algorithm.key
 the key material of the secret keypublic static HashFunction crc32c()
This function is best understood as a checksum rather than a true hash function.
public static HashFunction crc32()
To get the long
value equivalent to Checksum.getValue()
for a HashCode
produced by this function, use HashCode.padToLong()
.
This function is best understood as a checksum rather than a true hash function.
public static HashFunction adler32()
To get the long
value equivalent to Checksum.getValue()
for a HashCode
produced by this function, use HashCode.padToLong()
.
This function is best understood as a checksum rather than a true hash function.
public static HashFunction farmHashFingerprint64()
This is designed for generating persistent fingerprints of strings. It isn't cryptographically secure, but it produces a highquality hash with fewer collisions than some alternatives we've used in the past.
FarmHash fingerprints are encoded by HashCode.asBytes()
in littleendian order. This
means HashCode.asLong()
is guaranteed to return the same value that
farmhash::Fingerprint64() would for the same input (when compared using
UnsignedLongs
's encoding of 64bit unsigned numbers).
This function is best understood as a fingerprint rather than a true hash function.
public static int consistentHash(HashCode hashCode, int buckets)
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:
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.
public static int consistentHash(long input, int buckets)
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:
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.
public static HashCode combineOrdered(Iterable<HashCode> hashCodes)
IllegalArgumentException
 if hashCodes
is empty, or the hash codes do not all
have the same bit lengthpublic static HashCode combineUnordered(Iterable<HashCode> hashCodes)
IllegalArgumentException
 if hashCodes
is empty, or the hash codes do not all
have the same bit lengthpublic static HashFunction concatenating(HashFunction first, HashFunction second, HashFunction... rest)
For example, if you need 1024bit hash codes, you could join two sha512()
hash
functions together: Hashing.concatenating(Hashing.sha512(), Hashing.sha512())
.
public static HashFunction concatenating(Iterable<HashFunction> hashFunctions)
For example, if you need 1024bit hash codes, you could join two sha512()
hash
functions together: Hashing.concatenating(Hashing.sha512(), Hashing.sha512())
.
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