org.apache.hadoop.util.hash
Class Hash

java.lang.Object
  org.apache.hadoop.util.hash.Hash

Direct Known Subclasses:

JenkinsHash, MurmurHash

public abstract class Hash
extends Object

This class represents a common API for hashing functions.

Field Summary

static int	INVALID_HASH Constant to denote invalid hash type.
static int	JENKINS_HASH Constant to denote JenkinsHash.
static int	MURMUR_HASH Constant to denote MurmurHash.

Constructor Summary

Hash()

Method Summary

static int	getHashType(Configuration conf) This utility method converts the name of the configured hash type to a symbolic constant.
static Hash	getInstance(Configuration conf) Get a singleton instance of hash function of a type defined in the configuration.
static Hash	getInstance(int type) Get a singleton instance of hash function of a given type.
int	hash(byte[] bytes) Calculate a hash using all bytes from the input argument, and a seed of -1.
int	hash(byte[] bytes, int initval) Calculate a hash using all bytes from the input argument, and a provided seed value.
abstract int	hash(byte[] bytes, int length, int initval) Calculate a hash using bytes from 0 to length, and the provided seed value
static int	parseHashType(String name) This utility method converts String representation of hash function name to a symbolic constant.

Methods inherited from class java.lang.Object

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

Field Detail

INVALID_HASH

public static final int INVALID_HASH

Constant to denote invalid hash type.

See Also:

Constant Field Values

JENKINS_HASH

public static final int JENKINS_HASH

Constant to denote JenkinsHash.

See Also:

Constant Field Values

MURMUR_HASH

public static final int MURMUR_HASH

Constant to denote MurmurHash.

See Also:

Constant Field Values

Constructor Detail

Hash

public Hash()

Method Detail

parseHashType

public static int parseHashType(String name)

This utility method converts String representation of hash function name to a symbolic constant. Currently two function types are supported, "jenkins" and "murmur".

Parameters:

name - hash function name

Returns:

one of the predefined constants

getHashType

public static int getHashType(Configuration conf)

This utility method converts the name of the configured hash type to a symbolic constant.

Parameters:

conf - configuration

Returns:

one of the predefined constants

getInstance

public static Hash getInstance(int type)

Get a singleton instance of hash function of a given type.

Parameters:

type - predefined hash type

Returns:

hash function instance, or null if type is invalid

getInstance

public static Hash getInstance(Configuration conf)

Get a singleton instance of hash function of a type defined in the configuration.

Parameters:

conf - current configuration

Returns:

defined hash type, or null if type is invalid

hash

public int hash(byte[] bytes)

Calculate a hash using all bytes from the input argument, and a seed of -1.

Parameters:

bytes - input bytes

Returns:

hash value

hash

public int hash(byte[] bytes,
                int initval)

Calculate a hash using all bytes from the input argument, and a provided seed value.

Parameters:

bytes - input bytes

initval - seed value

Returns:

hash value

hash

public abstract int hash(byte[] bytes,
                         int length,
                         int initval)

Calculate a hash using bytes from 0 to length, and the provided seed value

Parameters:

bytes - input bytes

length - length of the valid bytes to consider

initval - seed value

Returns:

hash value