org.apache.hadoop.util.hash

类 JenkinsHash

java.lang.Object

org.apache.hadoop.util.hash.Hash

org.apache.hadoop.util.hash.JenkinsHash

public class JenkinsHash
extends Hash

Produces 32-bit hash for hash table lookup.

lookup3.c, by Bob Jenkins, May 2006, Public Domain.

 You can use this free for any purpose.  It's in the public domain.
 It has no warranty.
 

另请参阅:

lookup3.c, Hash Functions (and how this function compares to others such as CRC, MD?, etc, Has update on the Dr. Dobbs Article

字段概要

从类继承的字段 org.apache.hadoop.util.hash.Hash

INVALID_HASH, JENKINS_HASH, MURMUR_HASH

构造器概要

构造器

构造器和说明
JenkinsHash()

方法概要

方法

限定符和类型	方法和说明
static Hash	getInstance()
int	hash(byte[] key, int nbytes, int initval) taken from hashlittle() -- hash a variable-length key into a 32-bit value
static void	main(String[] args) Compute the hash of the specified file

从类继承的方法 org.apache.hadoop.util.hash.Hash

getHashType, getInstance, getInstance, hash, hash, parseHashType

从类继承的方法 java.lang.Object

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

构造器详细资料

JenkinsHash

public JenkinsHash()

方法详细资料

getInstance

public static Hash getInstance()

hash

public int hash(byte[] key,
       int nbytes,
       int initval)

taken from hashlittle() -- hash a variable-length key into a 32-bit value

指定者:

hash 在类中 Hash

参数:

key - the key (the unaligned variable-length array of bytes)

nbytes - number of bytes to include in hash

initval - can be any integer value

返回:

a 32-bit value. Every bit of the key affects every bit of the return value. Two keys differing by one or two bits will have totally different hash values.

The best hash table sizes are powers of 2. There is no need to do mod a prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask. For example, if you need only 10 bits, do h = (h & hashmask(10)); In which case, the hash table should have hashsize(10) elements.

If you are hashing n strings byte[][] k, do it like this: for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h);

By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this code any way you wish, private, educational, or commercial. It's free.

Use for hash table lookup, or anything where one collision in 2^^32 is acceptable. Do NOT use for cryptographic purposes.

main

public static void main(String[] args)
                 throws IOException

Compute the hash of the specified file

参数:

args - name of file to compute hash of.

抛出:

IOException