Hashing (Guava: Google Core Libraries for Java 19.0-rc3 API)

java.lang.Object
- com.google.common.hash.Hashing

```
@Beta
@CheckReturnValue
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

Author:

Kevin Bourrillion, Dimitris Andreou, Kurt Alfred Kluever

Method Summary

Methods
Modifier and Type	Method and 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(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 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`	`goodFastHash(int minimumBits)` Returns a general-purpose, temporary-use, non-cryptographic 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 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 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 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).
  - 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.
  - 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.
  - 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.
  - 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
  - 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

Class Hashing

Method Summary

Methods inherited from class java.lang.Object

Method Detail

goodFastHash

murmur3_32

murmur3_32

murmur3_128

murmur3_128

sipHash24

sipHash24

md5

sha1

sha256

sha384

sha512

crc32c

crc32

adler32

consistentHash

consistentHash

combineOrdered

combineUnordered

concatenating

concatenating