org.hsqldb.map

Class HashIndex

java.lang.Object

org.hsqldb.map.HashIndex

public class HashIndex
extends java.lang.Object

A chained bucket hash index implementation. hashTable and linkTable are arrays of signed integral types. This implementation uses int as the type but short or byte can be used for smaller index sizes (cardinality). hashTable[index] contains the pointer to the first node with (index == hash modulo hashTable.length) or -1 if there is no corresponding node. linkTable[{0,newNodePointer}] (the range between 0 and newNodePointer) contains either the pointer to the next node or -1 if there is no such node. reclaimedNodeIndex contains a pointer to an element of linkTable which is the first element in the list of reclaimed nodes (nodes no longer in index) or -1 if there is no such node. elemenet at and above linkTable[newNodePointer] have never been used as a node and their contents is not significant.

Since:

1.7.2

Constructor Summary

Constructors

Constructor and Description
HashIndex(int hashTableSize, int capacity, boolean fixedSize)

Method Summary

Modifier and Type	Method and Description
void	clear() Reset the index as empty.
int	getHashIndex(int hash)
int	getLookup(int hash) Return the array index for a hash.
int	getNextLookup(int lookup) This looks from a given node, so the parameter is always > -1.
int	linkNode(int index, int lastLookup) Link a new node to the end of the linked for a hash index.
boolean	removeEmptyNode(int lookup) Remove a node that has already been unlinked.
void	reset(int hashTableSize, int capacity) Reset the structure with a new size as empty.
void	resetTables()
void	unlinkNode(int index, int lastLookup, int lookup) Unlink a node from a linked list and link into the reclaimed list.

Methods inherited from class java.lang.Object

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

Constructor Detail

HashIndex

public HashIndex(int hashTableSize,
                 int capacity,
                 boolean fixedSize)

Method Detail

reset

public void reset(int hashTableSize,
                  int capacity)

Reset the structure with a new size as empty.

Parameters:

hashTableSize -

capacity -

resetTables

public void resetTables()

clear

public void clear()

Reset the index as empty.

getHashIndex

public int getHashIndex(int hash)

Parameters:

hash -

getLookup

public int getLookup(int hash)

Return the array index for a hash.

Parameters:

hash - the hash value used for indexing

Returns:

either -1 or the first node for this hash value

getNextLookup

public int getNextLookup(int lookup)

This looks from a given node, so the parameter is always > -1.

Parameters:

lookup - A valid node to look from

Returns:

either -1 or the next node from this node

linkNode

public int linkNode(int index,
                    int lastLookup)

Link a new node to the end of the linked for a hash index.

Parameters:

index - an index into hashTable

lastLookup - either -1 or the node to which the new node will be linked

Returns:

the new node

unlinkNode

public void unlinkNode(int index,
                       int lastLookup,
                       int lookup)

Unlink a node from a linked list and link into the reclaimed list.

Parameters:

index - an index into hashTable

lastLookup - either -1 or the node to which the target node is linked

lookup - the node to remove

removeEmptyNode

public boolean removeEmptyNode(int lookup)

Remove a node that has already been unlinked. This is not required for index operations. It is used only when the row needs to be removed from the data structures that store the actual indexed data and the nodes need to be contiguous.

Parameters:

lookup - the node to remove

Returns:

true if node found in unlinked state