jhplot.io

Class HDataBase

java.lang.Object

jhplot.io.HDataBase

public class HDataBase
extends Object

This raw-level database allows to store and retrieve objects. It associates a key of type String with each record. The keys will be limited to a maximum length, although the record data will not be limited. The record will consist of only one "blob" of binary data. The number of records is not fixed at creation time. The file can grow and shrink as records are inserted and removed. Because our index and record data will be stored in the same file, this restriction will cause us to add extra logic to dynamically increase the index space by reorganizing records. The database operations not depend on the number of records in the file. In other words, they'll be of constant order time with respect to file accesses. The index is small enough to load into memory. This will make it easier for our implementation to fulfill the requirement that dictates access time. The code is based on: http://www.javaworld.com/javaworld/jw-01-1999/jw-01-step.html

Field Summary

Fields

Modifier and Type	Field and Description
RecordsFile	recordsFile
RecordReader	rr
RecordWriter	rw

Constructor Summary

Constructors

Constructor and Description
HDataBase(String file) Open the database file for reading.
HDataBase(String file, String option) Create a new persistent database.

Method Summary

Modifier and Type	Method and Description
boolean	close() Close the file
Object	get(String key) Get object from the database using a key
Enumeration	getKeys() Returns an enumeration of all the keys in the database.
int	getRecords() Returns the current number of records in the database.
boolean	insert(String key, Object obj) Insert an object with a key
boolean	isExists(String key) Checks if there is a record belonging to the given key.
boolean	remove(String key) Remove object from the database using the key
boolean	update(Object ob, String key) Update the database with a new value

Methods inherited from class java.lang.Object

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

Field Detail

recordsFile

public RecordsFile recordsFile

rw

public RecordWriter rw

rr

public RecordReader rr

Constructor Detail

HDataBase

public HDataBase(String file,
                 String option)

Create a new persistent database. If file exists, and the option "w" is set, the old file will be removed!

Parameters:

file - File name

option - Option to create the file . If "w" - write a file (or read) file, if "r" only read created file.

HDataBase

public HDataBase(String file)

Open the database file for reading.

Parameters:

file - File name

Method Detail

getKeys

public Enumeration getKeys()

Returns an enumeration of all the keys in the database.

getRecords

public int getRecords()

Returns the current number of records in the database.

isExists

public boolean isExists(String key)

Checks if there is a record belonging to the given key.

insert

public boolean insert(String key,
                      Object obj)

Insert an object with a key

Parameters:

key - key for object

obj - Object for this key

Returns:

true if success

get

public Object get(String key)

Get object from the database using a key

Parameters:

key - Key to get the object

Returns:

Object

update

public boolean update(Object ob,
                      String key)

Update the database with a new value

Parameters:

ob - Object

key - key

Returns:

true if success

remove

public boolean remove(String key)

Remove object from the database using the key

Parameters:

key - input key

Returns:

true if success

close

public boolean close()

Close the file

Returns: