jdbm.recman

Class FileHeader

java.lang.Object

jdbm.recman.FileHeader

All Implemented Interfaces:

BlockView

class FileHeader
extends java.lang.Object
implements BlockView

This class represents a file header. It is a 1:1 representation of the data that appears in block 0 of a file.
The FileHeader is stored into a BlockIo.
The BlockIo will always contain the following bytes :

• [0..3] 0x1350 : a marker for a FILE_HEADER
• [4..11] : The BlockIo reference to the first FREE_PAGE ID
• [12..19] : The BlockIo reference to the last FREE_PAGE ID
• [20..27] : The BlockIo reference to the first USED_PAGE ID
• [28..35] : The BlockIo reference to the last USED_PAGE ID
• [36..43] : The BlockIo reference to the first TRANSLATION_PAGE ID
• [44..51] : The BlockIo reference to the last TRANSLATION_PAGE ID
• [52..59] : The BlockIo reference to the first FREELOGIDS_PAGE ID
• [60..67] : The BlockIo reference to the last FREELOGIDS_PAGE ID
• [68..71] : The BlockIo reference to the first FREEPHYSIDS_PAGE ID
• [72..79] : The BlockIo reference to the last FREEPHYSIDS_PAGE ID
• [80..87]* : The reference to the BlockIo which is the root for the data contained in this File. We may have more than one, but no more than 1014, if the BLOCK_SIZE is 8192

Field Summary

Fields

Modifier and Type	Field and Description
private BlockIo	block The BlockIo used to store the FileHeader
(package private) static int	NROOTS The number of "root" rowids available in the file.
private static short	O_LISTS Position of the Lists in the blockIo
private static short	O_MAGIC Position of the Magic number for FileHeader
private static int	O_ROOTS Position of the ROOTs in the blockIo

Constructor Summary

Constructors

Constructor and Description
FileHeader(BlockIo block, boolean isNew) Constructs a FileHeader object from a block.

Method Summary

Modifier and Type	Method and Description
(package private) long	getFirstOf(int list) Returns the first block of the indicated list
(package private) long	getLastOf(int list) Returns the last block of the indicated list
(package private) long	getRoot(int root) Returns the indicated root rowid.
private short	offsetOfFirst(int list) Returns the offset of the "first" block of the indicated list
private short	offsetOfLast(int list) Returns the offset of the "last" block of the indicated list
private short	offsetOfRoot(int root) Returns the offset of the indicated root
(package private) void	setFirstOf(int list, long value) Sets the first block of the indicated list
(package private) void	setLastOf(int list, long value) Sets the last block of the indicated list
(package private) void	setRoot(int root, long rowid) Sets the indicated root rowid.
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

O_MAGIC

private static final short O_MAGIC

Position of the Magic number for FileHeader

See Also:

Constant Field Values

O_LISTS

private static final short O_LISTS

Position of the Lists in the blockIo

See Also:

Constant Field Values

O_ROOTS

private static final int O_ROOTS

Position of the ROOTs in the blockIo

See Also:

Constant Field Values

block

private BlockIo block

The BlockIo used to store the FileHeader

NROOTS

static final int NROOTS

The number of "root" rowids available in the file.

See Also:

Constant Field Values

Constructor Detail

FileHeader

FileHeader(BlockIo block,
           boolean isNew)

Constructs a FileHeader object from a block.

Parameters:

block - The block that contains the file header

isNew - If true, the file header is for a new file.

Throws:

java.io.IOException - if the block is too short to keep the file header.

Method Detail

offsetOfFirst

private short offsetOfFirst(int list)

Returns the offset of the "first" block of the indicated list

offsetOfLast

private short offsetOfLast(int list)

Returns the offset of the "last" block of the indicated list

offsetOfRoot

private short offsetOfRoot(int root)

Returns the offset of the indicated root

getFirstOf

long getFirstOf(int list)

Returns the first block of the indicated list

setFirstOf

void setFirstOf(int list,
                long value)

Sets the first block of the indicated list

getLastOf

long getLastOf(int list)

Returns the last block of the indicated list

setLastOf

void setLastOf(int list,
               long value)

Sets the last block of the indicated list

getRoot

long getRoot(int root)

Returns the indicated root rowid. A root rowid is a special rowid that needs to be kept between sessions. It could conceivably be stored in a special file, but as a large amount of space in the block header is wasted anyway, it's more useful to store it where it belongs.

See Also:

NROOTS

setRoot

void setRoot(int root,
             long rowid)

Sets the indicated root rowid.

See Also:

getRoot(int), NROOTS

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object