jdbm.recman

Class PageHeader

java.lang.Object

jdbm.recman.PageHeader

All Implemented Interfaces:

BlockView

Direct Known Subclasses:

DataPage, FreeLogicalRowIdPage, FreePhysicalRowIdPage, TranslationPage

public class PageHeader
extends java.lang.Object
implements BlockView

This class represents a page header. It is the common superclass for all different page views. It contains the following information:

1. 2 bytes: the short block type code
2. 8 bytes: the long block id of the next block in the block list
3. 8 bytes: the long block id of the previous block in the block list
4. 4 bytes: the size of this page

The page header block view hence sees 18 bytes of page header data.

Field Summary

Fields

Modifier and Type	Field and Description
protected BlockIo	blockIo the page header block this view is associated with
private static short	O_MAGIC the page (BlockIo's type code) short magic code
private static short	O_NEXT the long block id of the next block in the block list
private static short	O_PREV the long block id of the previous block in the block list
protected static short	SIZE the size of this page header

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	PageHeader(BlockIo blockIo) Constructs a PageHeader object from a block
(package private)	PageHeader(BlockIo blockIo, short type) Constructs a new PageHeader of the indicated type.

Method Summary

Modifier and Type	Method and Description
(package private) short	getMagic()
(package private) long	getNext()
(package private) long	getPrev()
(package private) static PageHeader	getView(BlockIo blockIo) Factory method to create or return a page header for the indicated block.
private boolean	magicOk() Returns true if the magic corresponds with the fileHeader magic.
protected void	paranoiaMagicOk() For paranoia mode
(package private) void	setNext(long next) Sets the next blockIo.
(package private) void	setPrev(long prev) Sets the previous block.
(package private) void	setType(short type) Sets the type of the page header
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

the page (BlockIo's type code) short magic code

See Also:

Constant Field Values

O_NEXT

private static final short O_NEXT

the long block id of the next block in the block list

See Also:

Constant Field Values

O_PREV

private static final short O_PREV

the long block id of the previous block in the block list

See Also:

Constant Field Values

SIZE

protected static final short SIZE

the size of this page header

See Also:

Constant Field Values

blockIo

protected BlockIo blockIo

the page header block this view is associated with

Constructor Detail

PageHeader

protected PageHeader(BlockIo blockIo)

Constructs a PageHeader object from a block

Parameters:

blockIo - The block that contains the page header

Throws:

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

PageHeader

PageHeader(BlockIo blockIo,
           short type)

Constructs a new PageHeader of the indicated type. Used for newly created pages.

Method Detail

getView

static PageHeader getView(BlockIo blockIo)

Factory method to create or return a page header for the indicated block.

magicOk

private boolean magicOk()

Returns true if the magic corresponds with the fileHeader magic.

paranoiaMagicOk

protected void paranoiaMagicOk()

For paranoia mode

getMagic

short getMagic()

Returns:

The magic code (ie, the 2 first bytes of the inner BlockIo)

getNext

long getNext()

Returns:

the next block (ie the long at position 2 in the BlockIo)

setNext

void setNext(long next)

Sets the next blockIo.

Parameters:

The - next Block ID

getPrev

long getPrev()

Returns:

the previous block (ie the long at position 10 in the BlockIo)

setPrev

void setPrev(long prev)

Sets the previous block.

setType

void setType(short type)

Sets the type of the page header

Parameters:

type - The PageHeader type to store at position 0

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object