Package com.coyotegulch.jisp

Class HashIndex

java.lang.Object
com.coyotegulch.jisp.HashIndex
All Implemented Interfaces:
ObjectIndex
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:

  • Constructor Summary

    Constructors
    Constructor
    Description
    HashIndex(String name)
    Deprecated.
    Opens a file as a HashIndex.
    HashIndex(String name, int numBuckets, int maxRecords, KeyObject nullKey)
    Deprecated.
    Creates the file as a HashIndex.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    close()
    Deprecated.
     
    long
    findKey(KeyObject key)
    Deprecated.
    Find the position of the object associated with a given key.
    void
    insertKey(KeyObject key, long pos)
    Deprecated.
    Insert a key into the database, associating a record position with the given key.
    void
    optimize()
    Deprecated.
    Improves the performance of this HashIndex by optimizing the index contents.
    void
    removeKey(KeyObject key)
    Deprecated.
    Removes the given key from the index.
    void
    replaceKey(KeyObject key, long pos)
    Deprecated.
    Replace the reference pos for the given key.
    void
    storeKey(KeyObject key, long pos)
    Deprecated.
    If the key already exists, replace the reference pos for the given key.

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • HashIndex

      public HashIndex(String name, int numBuckets, int maxRecords, KeyObject nullKey) throws IOException, ClassNotFoundException
      Deprecated.
      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:

    • HashIndex

      public HashIndex(String name) throws IOException, ClassNotFoundException
      Deprecated.
      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 Details