@Beta @CheckReturnValue 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()

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()

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 
goodFastHash(int minimumBits)
Returns a generalpurpose, temporaryuse, noncryptographic hash function.

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
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()
Returns a hash function implementing the SHA1 algorithm (160 hash bits) by delegating to the
SHA1
MessageDigest . 
static HashFunction 
sha256()
Returns a hash function implementing the SHA256 algorithm (256 hash bits) by delegating to
the SHA256
MessageDigest . 
static HashFunction 
sha384()
Returns a hash function implementing the SHA384 algorithm (384 hash bits) by delegating to
the SHA384
MessageDigest . 
static HashFunction 
sha512()
Returns a hash function implementing the SHA512 algorithm (512 hash bits) by delegating to the
SHA512
MessageDigest . 
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.
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)
public static HashFunction md5()
MessageDigest
.public static HashFunction sha1()
MessageDigest
.public static HashFunction sha256()
MessageDigest
.public static HashFunction sha384()
MessageDigest
.public static HashFunction sha512()
MessageDigest
.public static HashFunction crc32c()
public static HashFunction crc32()
CRC32
Checksum
.
To get the long
value equivalent to Checksum.getValue()
for a
HashCode
produced by this function, use HashCode.padToLong()
.
public static HashFunction adler32()
Adler32
Checksum
.
To get the long
value equivalent to Checksum.getValue()
for a
HashCode
produced by this function, use HashCode.padToLong()
.
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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