org.helidb.lang.hasher
Class ConstantSizeValueHasher<T extends Comparable<T>>

java.lang.Object
  org.helidb.lang.hasher.ConstantSizeValueHasher<T>

Type Parameters:

T - The type of value hashed.

All Implemented Interfaces:

Hasher<T,T>

public class ConstantSizeValueHasher<T extends Comparable<T>>
extends Object
implements Hasher<T,T>

This is a generic value-preserving Hasher. It uses a Serializer for its serializing methods.

Since:

1.0

Author:

Karl Gustafsson

In_jar:

helidb-core

Constructor Summary

ConstantSizeValueHasher(Serializer<T> serializer)
Constructor.

Method Summary

T	fromBytes(byte[] barr) Interpret the serialized hash value.
int	getHashLength() Get the size of the hash in bytes.
T	hash(T o) Hash the supplied value.
boolean	isPreservingValues() Does the hashing operation not modify the hashed value at all? This is true if v.equals(hasher.hash(v)) for all values v accepted by the hasher.
byte[]	toBytes(T o) Serialize the hash to a byte array.

Methods inherited from class java.lang.Object

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

Constructor Detail

ConstantSizeValueHasher

public ConstantSizeValueHasher(Serializer<T> serializer)
                        throws IllegalArgumentException

Constructor.

Parameters:

serializer - The serializer used for the serializing methods.

Throws:

IllegalArgumentException - If the serializer does not produce values of a constant size.

Method Detail

isPreservingValues

public boolean isPreservingValues()

Description copied from interface: Hasher

Does the hashing operation not modify the hashed value at all? This is true if v.equals(hasher.hash(v)) for all values v accepted by the hasher.

Specified by:

isPreservingValues in interface Hasher<T extends Comparable<T>,T extends Comparable<T>>

Returns:

true, always.

getHashLength

public int getHashLength()

Description copied from interface: Hasher

Get the size of the hash in bytes. This is the size of the byte array created by Hasher.toBytes(Comparable) and accepted by Hasher.fromBytes(byte[]).

Specified by:

getHashLength in interface Hasher<T extends Comparable<T>,T extends Comparable<T>>

Returns:

The size of the hash, in number of bytes.

hash

public T hash(T o)
                             throws NullPointerException

Description copied from interface: Hasher

Hash the supplied value.

Hashing may be a fairly expensive operation, depending on the implementation. Clients should try to reuse the result from this method as much as possible.

Specified by:

hash in interface Hasher<T extends Comparable<T>,T extends Comparable<T>>

Parameters:

o - The value to hash.

Returns:

o

Throws:

NullPointerException - If o == null and the serializer does not support null values.

toBytes

public byte[] toBytes(T o)

Description copied from interface: Hasher

Serialize the hash to a byte array.

For a given Hasher object, the byte arrays returned by this method must always be of the same size.

Specified by:

toBytes in interface Hasher<T extends Comparable<T>,T extends Comparable<T>>

Parameters:

o - The hash to serialize.

Returns:

The serialized hash.

fromBytes

public T fromBytes(byte[] barr)

Description copied from interface: Hasher

Interpret the serialized hash value.

Specified by:

fromBytes in interface Hasher<T extends Comparable<T>,T extends Comparable<T>>

Parameters:

barr - The serialized hash value.

Returns:

The hash value.