com.coyotegulch.jisp

Class HashIndex

public class HashIndex extends Object implements ObjectIndex

Deprecated: As of Jisp versioon 2.5.0, the HashIndex class is deprecated; it will be replaced in Jisp 3.0 by a more efficient and simpler hash-based index.

HashIndex associates a key value with a reference to persistent data, using a disk-based hash table. The index assumes that the position of a serializable object is constant, regardless of the actual meaning of the long position. In general, the position represents the location (file pointer) of a Serializable object in an IndexedObjectDatabase.

Use the IndexedObjectDatabase.attachIndex method to attach a BTreeIndex to a database. A database updates all attached indexes when it writes or removes objects from its file.

This class should not be used in new code. It was originally design to illustrate algorithms, and it suffers from a number of performance problems. A better, more efficient hash-bvased index will be introduced in version 3.0 of Jisp.

See Also: ObjectIndex

Constructor Summary
HashIndex(String name, int numBuckets, int maxRecords, KeyObject nullKey)
Creates the file as a HashIndex.
HashIndex(String name)
Opens a file as a HashIndex.
Method Summary
voidclose()
longfindKey(KeyObject key)
Find the position of the object associated with a given key.
voidinsertKey(KeyObject key, long pos)
Insert a key into the database, associating a record position with the given key.
voidoptimize()
Improves the performance of this HashIndex by optimizing the index contents.
voidremoveKey(KeyObject key)
Removes the given key from the index.
voidreplaceKey(KeyObject key, long pos)
Replace the reference pos for the given key.
voidstoreKey(KeyObject key, long pos)
If the key already exists, replace the reference pos for the given key.

Constructor Detail

HashIndex

public HashIndex(String name, int numBuckets, int maxRecords, KeyObject nullKey)
Creates the file as a HashIndex. The initial length of each list is based on numBuckets and macRecords. The null key is a "blank" key; obtain a null key for any KeyObject type by calling the KeyObject.makeNullKey method.

Parameters: name The name of the external index file to be opened. numBuckets The number of lists in the hash table; this is also known as the "hash factor." Use prime numbers to limit the number of collisions and increase the efficiency of the index. maxRecords The expected number of records to be indexed. This is not a limit on the index size; the index will expand to handle up to 2 billion records. However, the best performance is obtained by setting maxRecords to a value that reflects the expected size of the database. nullKey The null key serves two purposes: to identify a blank table entry, and to perform type-checking on new keys added to the index. All keys added to the index must have the same type as nullkey.

Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type

See Also: KeyObject

HashIndex

public HashIndex(String name)
Opens a file as a HashIndex.

Parameters: name The name of the external index file to be opened.

Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type

Method Detail

close

public void close()

findKey

public long findKey(KeyObject key)
Find the position of the object associated with a given key.

Parameters: key A key identifying the record to be read.

Returns: The position of the record associated with key.

Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type KeyNotFound when the specified key can not be found in the index

See Also: KeyNotFound KeyObject

insertKey

public void insertKey(KeyObject key, long pos)
Insert a key into the database, associating a record position with the given key.

Parameters: key A key identifying the record to be read. pos File position of record associated with key

Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type DuplicateKey when inserting a duplicate key into an index that does not support duplicates

See Also: DuplicateKey KeyObject

optimize

public void optimize()
Improves the performance of this HashIndex by optimizing the index contents.

removeKey

public void removeKey(KeyObject key)
Removes the given key from the index.

Parameters: key A key identifying the record to be read.

Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type KeyNotFound when the specified key can not be found in the index

See Also: KeyNotFound KeyObject

replaceKey

public void replaceKey(KeyObject key, long pos)
Replace the reference pos for the given key.

Parameters: key A key identifying the record to be read. pos File position of record associated with key

Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type KeyNotFound when the specified key can not be found in the index

See Also: KeyNotFound KeyObject

storeKey

public void storeKey(KeyObject key, long pos)
If the key already exists, replace the reference pos for the given key. Otherwise, insert a key into the database, associating a record position with the given key.

Parameters: key A key identifying the record to be read. pos File position of record associated with key

Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type

See Also: KeyObject