Package org.apache.hadoop.util.hash

Class Hash

java.lang.Object

org.apache.hadoop.util.hash.Hash

Direct Known Subclasses:

JenkinsHash, MurmurHash

@Private
@Unstable
public abstract class Hash
extends java.lang.Object

This class represents a common API for hashing functions.

Field Summary

Fields

Modifier and Type	Field	Description
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

Constructors

Constructor	Description
Hash()

Method Summary

Modifier and Type	Method	Description
static int	getHashType(Configuration conf)	This utility method converts the name of the configured hash type to a symbolic constant.
static Hash	getInstance(int type)	Get a singleton instance of hash function of a given type.
static Hash	getInstance(Configuration conf)	Get a singleton instance of hash function of a type defined in the configuration.
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(java.lang.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(java.lang.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