BPage (JDBM JavaDoc)

java.lang.Object
- jdbm.btree.BPage

All Implemented Interfaces:

java.io.Serializable, Serializer
```
public final class BPage
extends java.lang.Object
implements Serializer
```
Page of a Btree.
The page contains a number of key-value pairs. Keys are ordered to allow dichotomic search.
If the page is a leaf page, the keys and values are user-defined and represent entries inserted by the user.
If the page is non-leaf, each key represents the greatest key in the underlying BPages and the values are recids pointing to the children BPages. The only exception is the rightmost BPage, which is considered to have an "infinite" key value, meaning that any insert will be to the left of this pseudo-key

Version:

$Id: BPage.java,v 1.6 2003/09/21 15:46:59 boisvert Exp $

Author:

Alex Boisvert

See Also:
Serialized Form

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`(package private) static class`	`BPage.Browser` PRIVATE INNER CLASS Browser to traverse leaf BPages.
`(package private) static class`	`BPage.InsertResult` STATIC INNER CLASS Result from insert() method call
`(package private) static class`	`BPage.RemoveResult` STATIC INNER CLASS Result from remove() method call

Field Summary

Fields
Modifier and Type	Field and Description
`(package private) BTree`	`_btree` Parent B+Tree.
`protected long[]`	`_children` Children pages (recids) associated with keys.
`protected int`	`_first` Index of first used item at the page
`protected boolean`	`_isLeaf` Flag indicating if this is a leaf BPage.
`protected java.lang.Object[]`	`_keys` Keys of children nodes
`protected long`	`_next` Next leaf BPage (only if this BPage is a leaf)
`protected long`	`_previous` Previous leaf BPage (only if this BPage is a leaf)
`protected long`	`_recid` This BPage's record ID in the PageManager.
`protected java.lang.Object[]`	`_values` Values associated with keys.
`(package private) static long`	`serialVersionUID` Version id for serialization.

Constructor Summary

Constructors
Constructor and Description
`BPage()` No-argument constructor used by serialization.
`BPage(BTree btree, boolean isLeaf)` Overflow page constructor.
`BPage(BTree btree, BPage root, BPage overflow)` Root page overflow constructor
`BPage(BTree btree, java.lang.Object key, java.lang.Object value)` Root page (first insert) constructor.

Method Summary

Methods
Modifier and Type	Method and Description
`(package private) void`	`assertConsistencyRecursive(int height)` Recursively assert the ordering of the BPage entries on this page and sub-pages.
`(package private) BPage`	`childBPage(int index)` Return the child BPage at given index.
`java.lang.Object`	`deserialize(byte[] serialized)` Deserialize the content of an object from a byte array.
`(package private) void`	`dumpRecursive(int height, int level)` Recursively dump the state of the BTree on screen.
`(package private) TupleBrowser`	`find(int height, java.lang.Object key)` Find the object associated with the given key.
`(package private) TupleBrowser`	`findFirst()` Find first entry and return a browser positioned before it.
`(package private) java.lang.Object`	`getLargestKey()` Get largest key under this BPage.
`(package private) BPage.InsertResult`	`insert(int height, java.lang.Object key, java.lang.Object value, boolean replace)` Insert the given key and value.
`(package private) boolean`	`isEmpty()` Return true if BPage is empty.
`(package private) boolean`	`isFull()` Return true if BPage is full.
`(package private) static byte[]`	`readByteArray(java.io.ObjectInput in)`
`(package private) BPage.RemoveResult`	`remove(int height, java.lang.Object key)` Remove the entry associated with the given key.
`byte[]`	`serialize(java.lang.Object obj)` Serialize the content of an object into a byte array.
`(package private) static void`	`writeByteArray(java.io.ObjectOutput out, byte[] buf)`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - serialVersionUID
```
static final long serialVersionUID
```
    Version id for serialization.
    
    See Also:
    Constant Field Values
  - _btree
```
transient BTree _btree
```
    Parent B+Tree.
  - _recid
```
protected transient long _recid
```
    This BPage's record ID in the PageManager.
  - _isLeaf
```
protected boolean _isLeaf
```
    Flag indicating if this is a leaf BPage.
  - _keys
```
protected java.lang.Object[] _keys
```
    Keys of children nodes
  - _values
```
protected java.lang.Object[] _values
```
    Values associated with keys. (Only valid if leaf BPage)
  - _children
```
protected long[] _children
```
    Children pages (recids) associated with keys. (Only valid if non-leaf BPage)
  - _first
```
protected int _first
```
    Index of first used item at the page
  - _previous
```
protected long _previous
```
    Previous leaf BPage (only if this BPage is a leaf)
  - _next
```
protected long _next
```
    Next leaf BPage (only if this BPage is a leaf)
- Constructor Detail
  - BPage
```
public BPage()
```
    No-argument constructor used by serialization.
  - BPage
```
BPage(BTree btree,
     BPage root,
     BPage overflow)
throws java.io.IOException
```
    Root page overflow constructor
    
    Throws:
    
    java.io.IOException
  - BPage
```
BPage(BTree btree,
     java.lang.Object key,
     java.lang.Object value)
throws java.io.IOException
```
    Root page (first insert) constructor.
    
    Throws:
    
    java.io.IOException
  - BPage
```
BPage(BTree btree,
     boolean isLeaf)
throws java.io.IOException
```
    Overflow page constructor. Creates an empty BPage.
    
    Throws:
    
    java.io.IOException
- Method Detail
  - getLargestKey
```
java.lang.Object getLargestKey()
```
    Get largest key under this BPage. Null is considered to be the greatest possible key.
  - isEmpty
```
boolean isEmpty()
```
    Return true if BPage is empty.
  - isFull
```
boolean isFull()
```
    Return true if BPage is full.
  - find
```
TupleBrowser find(int height,
                java.lang.Object key)
            throws java.io.IOException
```
    Find the object associated with the given key.
    
    Parameters:
    height - Height of the current BPage (zero is leaf page)
    key - The key
    
    Returns:
    TupleBrowser positionned just before the given key, or before next greater key if key isn't found.
    
    Throws:
    
    java.io.IOException
  - findFirst
```
TupleBrowser findFirst()
                 throws java.io.IOException
```
    Find first entry and return a browser positioned before it.
    
    Returns:
    TupleBrowser positionned just before the first entry.
    
    Throws:
    
    java.io.IOException
  - insert
```
BPage.InsertResult insert(int height,
                        java.lang.Object key,
                        java.lang.Object value,
                        boolean replace)
                    throws java.io.IOException
```
    Insert the given key and value.
    Since the Btree does not support duplicate entries, the caller must specify whether to replace the existing value.
    
    Parameters:
    height - Height of the current BPage (zero is leaf page)
    key - Insert key
    value - Insert value
    replace - Set to true to replace the existing value, if one exists.
    
    Returns:
    Insertion result containing existing value OR a BPage if the key was inserted and provoked a BPage overflow.
    
    Throws:
    
    java.io.IOException
  - remove
```
BPage.RemoveResult remove(int height,
                        java.lang.Object key)
                    throws java.io.IOException
```
    Remove the entry associated with the given key.
    
    Parameters:
    height - Height of the current BPage (zero is leaf page)
    key - Removal key
    
    Returns:
    Remove result object
    
    Throws:
    
    java.io.IOException
  - childBPage
```
BPage childBPage(int index)
           throws java.io.IOException
```
    Return the child BPage at given index.
    
    Throws:
    
    java.io.IOException
  - readByteArray
```
static byte[] readByteArray(java.io.ObjectInput in)
                     throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - writeByteArray
```
static void writeByteArray(java.io.ObjectOutput out,
                  byte[] buf)
                    throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - dumpRecursive
```
void dumpRecursive(int height,
                 int level)
             throws java.io.IOException
```
    Recursively dump the state of the BTree on screen. This is used for debugging purposes only.
    
    Throws:
    
    java.io.IOException
  - assertConsistencyRecursive
```
void assertConsistencyRecursive(int height)
                          throws java.io.IOException
```
    Recursively assert the ordering of the BPage entries on this page and sub-pages. This is used for testing purposes only.
    
    Throws:
    
    java.io.IOException
  - deserialize
```
public java.lang.Object deserialize(byte[] serialized)
                             throws java.io.IOException
```
    Deserialize the content of an object from a byte array.
    
    Specified by:
    
    deserialize in interface Serializer
    
    Parameters:
    serialized - Byte array representation of the object
    
    Returns:
    deserialized object
    
    Throws:
    
    java.io.IOException
  - serialize
```
public byte[] serialize(java.lang.Object obj)
                 throws java.io.IOException
```
    Serialize the content of an object into a byte array.
    
    Specified by:
    
    serialize in interface Serializer
    
    Parameters:
    obj - Object to serialize
    
    Returns:
    a byte array representing the object's state
    
    Throws:
    
    java.io.IOException

Class BPage

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

serialVersionUID

_btree

_recid

_isLeaf

_keys

_values

_children

_first

_previous

_next

Constructor Detail

BPage

BPage

BPage

BPage

Method Detail

getLargestKey

isEmpty

isFull

find

findFirst

insert

remove

childBPage

readByteArray

writeByteArray

dumpRecursive

assertConsistencyRecursive

deserialize

serialize