Package com.coyotegulch.jisp
Class HashIndex
java.lang.Object
com.coyotegulch.jisp.HashIndex
- All Implemented Interfaces:
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:
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
Deprecated.long
Deprecated.Find the position of the object associated with a given key.void
Deprecated.Insert a key into the database, associating a record position with the given key.void
optimize()
Deprecated.Improves the performance of thisHashIndex
by optimizing the index contents.void
Deprecated.Removes the given key from the index.void
replaceKey
(KeyObject key, long pos) Deprecated.Replace the reference pos for the given key.void
Deprecated.If the key already exists, replace the reference pos for the given key.
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Constructor Details
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HashIndex
public HashIndex(String name, int numBuckets, int maxRecords, KeyObject nullKey) throws IOException, ClassNotFoundException Deprecated.Creates the file as aHashIndex
. The initial length of each list is based onnumBuckets
andmacRecords
. The null key is a "blank" key; obtain a null key for anyKeyObject
type by calling theKeyObject.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 isnot
a limit on the index size; the index will expand to handle up to 2 billion records. However, the best performance is obtained by settingmaxRecords
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 asnullkey
.- Throws:
IOException
- when an I/O exception is thrown by an underlying java.io.* classClassNotFoundException
- for a casting error, usually when a persistent object or index does match the expected type- See Also:
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HashIndex
Deprecated.Opens a file as aHashIndex
.- 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.* classClassNotFoundException
- for a casting error, usually when a persistent object or index does match the expected type
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Method Details
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insertKey
public void insertKey(KeyObject key, long pos) throws IOException, DuplicateKey, ClassNotFoundException Deprecated.Insert a key into the database, associating a record position with the given key.- Specified by:
insertKey
in interfaceObjectIndex
- 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.* classClassNotFoundException
- for a casting error, usually when a persistent object or index does match the expected typeDuplicateKey
- when inserting a duplicate key into an index that does not support duplicates- See Also:
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replaceKey
Deprecated.Replace the reference pos for the given key.- Specified by:
replaceKey
in interfaceObjectIndex
- 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.* classClassNotFoundException
- for a casting error, usually when a persistent object or index does match the expected typeKeyNotFound
- when the specified key can not be found in the index- See Also:
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storeKey
Deprecated.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.- Specified by:
storeKey
in interfaceObjectIndex
- 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.* classClassNotFoundException
- for a casting error, usually when a persistent object or index does match the expected type- See Also:
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findKey
Deprecated.Find the position of the object associated with a given key.- Specified by:
findKey
in interfaceObjectIndex
- 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.* classClassNotFoundException
- for a casting error, usually when a persistent object or index does match the expected typeKeyNotFound
- when the specified key can not be found in the index- See Also:
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removeKey
Deprecated.Removes the given key from the index.- Specified by:
removeKey
in interfaceObjectIndex
- Parameters:
key
- A key identifying the record to be read.- Throws:
IOException
- when an I/O exception is thrown by an underlying java.io.* classClassNotFoundException
- for a casting error, usually when a persistent object or index does match the expected typeKeyNotFound
- when the specified key can not be found in the index- See Also:
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optimize
Deprecated.Improves the performance of thisHashIndex
by optimizing the index contents.- Throws:
IOException
ClassNotFoundException
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close
Deprecated.- Throws:
IOException
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