org.klomp.snark

Class BitField

java.lang.Object

org.klomp.snark.BitField

public class BitField
extends Object

Container of a byte array representing set and unset bits for torrent piece availability.

This class manages a bit field where each bit represents whether a particular piece of a torrent is available (set) or not available (unset). It's used to:

• Track which pieces a peer has available
• Track which pieces the local client has downloaded
• Determine which pieces are still needed
• Optimize piece selection strategies

The bit field is stored efficiently in a byte array, with 8 bits per byte.

Constructor Summary

Constructors

Constructor and Description
BitField(byte[] bitfield, int size) Creates a new BitField that represents the given number of bits as set by the given byte array.
BitField(int size) Creates a new BitField that represents the given number of unset bits.

Method Summary

Modifier and Type	Method and Description
void	clear(int bit) Sets the given bit to false.
boolean	complete() Returns true if all bits are set.
int	count() Returns the number of set bits.
boolean	equals(Object o) Compares this BitField to another object for equality.
boolean	get(int bit) Returns true if the bit is set or false if it is not.
byte[]	getFieldBytes() Returns the actual byte array used.
int	hashCode() Returns a hash code value for this BitField.
void	set(int bit) Sets the given bit to true.
void	setAll() Sets all bits to true.
int	size() Returns the size of the BitField.
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

BitField

public BitField(byte[] bitfield,
                int size)

Creates a new BitField that represents the given number of bits as set by the given byte array. This will make a copy of the array. Extra bytes will be ignored.

Parameters:

bitfield - the byte array containing the bit field data

size - the number of bits represented

Throws:

IndexOutOfBoundsException - if the byte array is not large enough

BitField

public BitField(int size)

Creates a new BitField that represents the given number of unset bits.

Parameters:

size - the number of bits in the bit field

Method Detail

clear

public void clear(int bit)

Sets the given bit to false.

Parameters:

bit - the bit index to clear

Throws:

IndexOutOfBoundsException - if bit is smaller then zero or bigger then or equal to size

complete

public boolean complete()

Returns true if all bits are set.

Returns:

true if all bits are set (bit field is complete), false otherwise

count

public int count()

Returns the number of set bits.

Returns:

the count of bits that are set to true

equals

public boolean equals(Object o)

Compares this BitField to another object for equality.

Overrides:

equals in class Object

Parameters:

o - the object to compare with

Returns:

true if the objects are equal, false otherwise

get

public boolean get(int bit)

Returns true if the bit is set or false if it is not.

Parameters:

bit - the bit index to check

Returns:

true if the bit is set, false otherwise

Throws:

IndexOutOfBoundsException - if bit is smaller then zero or bigger then or equal to size

getFieldBytes

public byte[] getFieldBytes()

Returns the actual byte array used. Changes to this array affect this BitField. Note that some bits at the end of the byte array are supposed to be always unset if they represent bits bigger then the size of the bitfield.

Caller should synchronize on this and copy!

Returns:

the internal byte array representing the bit field

hashCode

public int hashCode()

Returns a hash code value for this BitField.

Overrides:

hashCode in class Object

Returns:

a hash code value for this BitField

set

public void set(int bit)

Sets the given bit to true.

Parameters:

bit - the bit index to set

Throws:

IndexOutOfBoundsException - if bit is smaller then zero or bigger then or equal to size

setAll

public void setAll()

Sets all bits to true.

size

public int size()

Returns the size of the BitField. The returned value is one bigger then the last valid bit number (since bit numbers are counted from zero).

Returns:

the number of bits in the bit field

toString

public String toString()

Overrides:

toString in class Object