com.googlecode.javaewah.datastructure
Class BitSet

java.lang.Object
  com.googlecode.javaewah.datastructure.BitSet

All Implemented Interfaces:

Externalizable, Serializable, Cloneable, Iterable<Integer>

public class BitSet
extends Object
implements Cloneable, Iterable<Integer>, Externalizable

This is an optimized version of Java's BitSet. In many cases, it can be used as a drop-in replacement. It differs from the basic Java BitSet class in the following ways:

• You can iterate over set bits using a simpler syntax for(int bs: mybitset).
• You can compute the cardinality of an intersection and union without writing it out or modifying your BitSets (see methods such as andcardinality).
• You can recover wasted memory with trim().

Since:

0.8.0

Author:

Daniel Lemire

See Also:

Serialized Form

Constructor Summary

BitSet(int sizeinbits)
Construct a bitset with the specified number of bits (initially all false).

Method Summary

void	and(BitSet bs) Compute bitwise AND.
int	andcardinality(BitSet bs) Compute cardinality of bitwise AND.
void	andNot(BitSet bs) Compute bitwise AND NOT.
int	andNotcardinality(BitSet bs) Compute cardinality of bitwise AND NOT.
int	cardinality() Compute the number of bits set to 1
void	clear() Reset all bits to false.
BitSet	clone()
boolean	empty() Check whether a bitset contains a set bit.
boolean	equals(Object o)
boolean	get(int i)
int	hashCode()
boolean	intersects(BitSet bs) Checks whether two bitsets intersect.
IntIterator	intIterator() Iterate over the set bits
Iterator<Integer>	iterator()
int	nextSetBit(int i) Usage: for(int i=bs.nextSetBit(0); i>=0; i=bs.nextSetBit(i+1)) { operate on index i here }
int	nextUnsetBit(int i) Usage: for(int i=bs.nextUnsetBit(0); i>=0; i=bs.nextUnsetBit(i+1)) { operate on index i here }
void	or(BitSet bs) Compute bitwise OR.
int	orcardinality(BitSet bs) Compute cardinality of bitwise OR.
void	readExternal(ObjectInput in)
void	resize(int sizeinbits) Resize the bitset
void	set(int i) Set to true
void	set(int i, boolean b)
int	size() Query the size
void	trim() Recovers wasted memory
void	unset(int i) Set to false
IntIterator	unsetIntIterator() Iterate over the unset bits
void	writeExternal(ObjectOutput out)
void	xor(BitSet bs) Compute bitwise XOR.
int	xorcardinality(BitSet bs) Compute cardinality of bitwise XOR.

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BitSet

public BitSet(int sizeinbits)

Construct a bitset with the specified number of bits (initially all false). The number of bits is rounded up to the nearest multiple of 64.

Parameters:

sizeinbits - the size in bits

Method Detail

and

public void and(BitSet bs)

Compute bitwise AND.

Parameters:

bs - other bitset

andcardinality

public int andcardinality(BitSet bs)

Compute cardinality of bitwise AND. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.

Parameters:

bs - other bitset

Returns:

cardinality

andNot

public void andNot(BitSet bs)

Compute bitwise AND NOT. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.

Parameters:

bs - other bitset

andNotcardinality

public int andNotcardinality(BitSet bs)

Compute cardinality of bitwise AND NOT.

Parameters:

bs - other bitset

Returns:

cardinality

cardinality

public int cardinality()

Compute the number of bits set to 1

Returns:

the number of bits

clear

public void clear()

Reset all bits to false. This might be wasteful: a better approach is to create a new empty bitmap.

clone

public BitSet clone()

Overrides:

clone in class Object

equals

public boolean equals(Object o)

Overrides:

equals in class Object

empty

public boolean empty()

Check whether a bitset contains a set bit.

Returns:

true if no set bit is found

get

public boolean get(int i)

Parameters:

i - index

Returns:

value of the bit

hashCode

public int hashCode()

Overrides:

hashCode in class Object

intIterator

public IntIterator intIterator()

Iterate over the set bits

Returns:

an iterator

iterator

public Iterator<Integer> iterator()

Specified by:

iterator in interface Iterable<Integer>

intersects

public boolean intersects(BitSet bs)

Checks whether two bitsets intersect.

Parameters:

bs - other bitset

Returns:

true if they have a non-empty intersection (result of AND)

nextSetBit

public int nextSetBit(int i)

Usage: for(int i=bs.nextSetBit(0); i>=0; i=bs.nextSetBit(i+1)) { operate on index i here }

Parameters:

i - current set bit

Returns:

next set bit or -1

nextUnsetBit

public int nextUnsetBit(int i)

Usage: for(int i=bs.nextUnsetBit(0); i>=0; i=bs.nextUnsetBit(i+1)) { operate on index i here }

Parameters:

i - current unset bit

Returns:

next unset bit or -1

or

public void or(BitSet bs)

Compute bitwise OR. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.

Parameters:

bs - other bitset

orcardinality

public int orcardinality(BitSet bs)

Compute cardinality of bitwise OR. BitSets are not modified.

Parameters:

bs - other bitset

Returns:

cardinality

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

resize

public void resize(int sizeinbits)

Resize the bitset

Parameters:

sizeinbits - new number of bits

set

public void set(int i)

Set to true

Parameters:

i - index of the bit

set

public void set(int i,
                boolean b)

Parameters:

i - index

b - value of the bit

size

public int size()

Query the size

Returns:

the size in bits.

trim

public void trim()

Recovers wasted memory

unset

public void unset(int i)

Set to false

Parameters:

i - index of the bit

unsetIntIterator

public IntIterator unsetIntIterator()

Iterate over the unset bits

Returns:

an iterator

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

xor

public void xor(BitSet bs)

Compute bitwise XOR. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.

Parameters:

bs - other bitset

xorcardinality

public int xorcardinality(BitSet bs)

Compute cardinality of bitwise XOR. BitSets are not modified.

Parameters:

bs - other bitset

Returns:

cardinality