java.lang.Object
- org.apache.lucene.search.DocIdSet
- - org.apache.lucene.util.OpenBitSet

All Implemented Interfaces:

Cloneable, Bits

Direct Known Subclasses:

OpenBitSetDISI
```
public class OpenBitSet
extends DocIdSet
implements Bits, Cloneable
```
An "open" BitSet implementation that allows direct access to the array of words storing the bits.
Unlike java.util.bitset, the fact that bits are packed into an array of longs is part of the interface. This allows efficient implementation of other algorithms by someone other than the author. It also allows one to efficiently implement alternate serialization or interchange formats.
OpenBitSet is faster than java.util.BitSet in most operations and *much* faster at calculating cardinality of sets and results of set operations. It can also handle sets of larger cardinality (up to 64 * 2**32-1)
The goals of OpenBitSet are the fastest implementation possible, and maximum code reuse. Extra safety and encapsulation may always be built on top, but if that's built in, the cost can never be removed (and hence people re-implement their own version in order to get better performance). If you want a "safe", totally encapsulated (and slower and limited) BitSet class, use java.util.BitSet.

Performance Results
Test system: Pentium 4, Sun Java 1.5_06 -server -Xbatch -Xmx64M
BitSet size = 1,000,000
Results are java.util.BitSet time divided by OpenBitSet time.

cardinality intersect_count union nextSetBit get iterator

50% full 3.36 3.96 1.44 1.46 1.99 1.58

1% full 3.31 3.90 1.04 0.99

Test system: AMD Opteron, 64 bit linux, Sun Java 1.5_06 -server -Xbatch -Xmx64M
BitSet size = 1,000,000
Results are java.util.BitSet time divided by OpenBitSet time.

cardinality intersect_count union nextSetBit get iterator

50% full 2.50 3.50 1.00 1.03 1.12 1.25

1% full 2.51 3.49 1.00 1.02

Nested Class Summary
- Nested classes/interfaces inherited from interface org.apache.lucene.util.Bits
  Bits.MatchAllBits, Bits.MatchNoBits

Field Summary

Fields
Modifier and Type Field Description

protected long[] bits

protected int wlen
- Fields inherited from interface org.apache.lucene.util.Bits
  EMPTY_ARRAY

Constructor Summary

Constructors
Constructor	Description
`OpenBitSet()`	Constructor: allocates enough space for 64 bits.
`OpenBitSet(long numBits)`	Constructs an OpenBitSet large enough to hold `numBits`.
`OpenBitSet(long[] bits, int numWords)`	Constructs an OpenBitSet from an existing long[].

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`and(OpenBitSet other)`
`void`	`andNot(OpenBitSet other)`
`static long`	`andNotCount(OpenBitSet a, OpenBitSet b)`	Returns the popcount or cardinality of "a and not b" or "intersection(a, not(b))".
`Bits`	`bits()`	Optionally provides a `Bits` interface for random access to matching documents.
`static int`	`bits2words(long numBits)`	returns the number of 64 bit words it would take to hold numBits
`long`	`capacity()`	Returns the current capacity in bits (1 greater than the index of the last bit)
`long`	`cardinality()`
`void`	`clear(int startIndex, int endIndex)`	Clears a range of bits.
`void`	`clear(long index)`	clears a bit, allowing access beyond the current set size without changing the size.
`void`	`clear(long startIndex, long endIndex)`	Clears a range of bits.
`OpenBitSet`	`clone()`
`void`	`ensureCapacity(long numBits)`	Ensure that the long[] is big enough to hold numBits, expanding it if necessary.
`void`	`ensureCapacityWords(int numWords)`	Expand the long[] with the size given as a number of words (64 bit longs).
`boolean`	`equals(Object o)`	returns true if both sets have the same bits set
`protected int`	`expandingWordNum(long index)`
`void`	`fastClear(int index)`	clears a bit.
`void`	`fastClear(long index)`	clears a bit.
`void`	`fastFlip(int index)`	flips a bit.
`void`	`fastFlip(long index)`	flips a bit.
`boolean`	`fastGet(int index)`	Returns true or false for the specified bit index.
`boolean`	`fastGet(long index)`	Returns true or false for the specified bit index.
`void`	`fastSet(int index)`	Sets the bit at the specified index.
`void`	`fastSet(long index)`	Sets the bit at the specified index.
`void`	`flip(long index)`	flips a bit, expanding the set size if necessary
`void`	`flip(long startIndex, long endIndex)`	Flips a range of bits, expanding the set size if necessary
`boolean`	`flipAndGet(int index)`	flips a bit and returns the resulting bit value.
`boolean`	`flipAndGet(long index)`	flips a bit and returns the resulting bit value.
`boolean`	`get(int index)`	Returns true or false for the specified bit index.
`boolean`	`get(long index)`	Returns true or false for the specified bit index
`boolean`	`getAndSet(int index)`	Sets a bit and returns the previous value.
`boolean`	`getAndSet(long index)`	Sets a bit and returns the previous value.
`int`	`getBit(int index)`	returns 1 if the bit is set, 0 if not.
`long[]`	`getBits()`	Expert: returns the long[] storing the bits
`int`	`getNumWords()`	Expert: gets the number of longs in the array that are in use
`int`	`hashCode()`
`void`	`intersect(OpenBitSet other)`	this = this AND other
`static long`	`intersectionCount(OpenBitSet a, OpenBitSet b)`	Returns the popcount or cardinality of the intersection of the two sets.
`boolean`	`intersects(OpenBitSet other)`	returns true if the sets have any elements in common
`boolean`	`isCacheable()`	This DocIdSet implementation is cacheable.
`boolean`	`isEmpty()`	Returns true if there are no set bits
`DocIdSetIterator`	`iterator()`	Provides a `DocIdSetIterator` to access the set.
`int`	`length()`	Returns the number of bits in this set
`int`	`nextSetBit(int index)`	Returns the index of the first set bit starting at the index specified.
`long`	`nextSetBit(long index)`	Returns the index of the first set bit starting at the index specified.
`void`	`or(OpenBitSet other)`
`int`	`prevSetBit(int index)`	Returns the index of the first set bit starting downwards at the index specified.
`long`	`prevSetBit(long index)`	Returns the index of the first set bit starting downwards at the index specified.
`void`	`remove(OpenBitSet other)`	Remove all elements set in other.
`void`	`set(long index)`	sets a bit, expanding the set size if necessary
`void`	`set(long startIndex, long endIndex)`	Sets a range of bits, expanding the set size if necessary
`long`	`size()`	Returns the current capacity of this set.
`void`	`trimTrailingZeros()`	Lowers numWords, the number of words in use, by checking for trailing zero words.
`void`	`union(OpenBitSet other)`	this = this OR other
`static long`	`unionCount(OpenBitSet a, OpenBitSet b)`	Returns the popcount or cardinality of the union of the two sets.
`void`	`xor(OpenBitSet other)`	this = this XOR other
`static long`	`xorCount(OpenBitSet a, OpenBitSet b)`	Returns the popcount or cardinality of the exclusive-or of the two sets.

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

- Field Detail
  - bits
```
protected long[] bits
```
  - wlen
```
protected int wlen
```
- Constructor Detail
  - OpenBitSet
```
public OpenBitSet(long numBits)
```
    Constructs an OpenBitSet large enough to hold numBits.
  - OpenBitSet
```
public OpenBitSet()
```
    Constructor: allocates enough space for 64 bits.
  - OpenBitSet
```
public OpenBitSet(long[] bits,
                  int numWords)
```
    Constructs an OpenBitSet from an existing long[].
    The first 64 bits are in long[0], with bit index 0 at the least significant bit, and bit index 63 at the most significant. Given a bit index, the word containing it is long[index/64], and it is at bit number index%64 within that word.
    numWords are the number of elements in the array that contain set bits (non-zero longs). numWords should be <= bits.length, and any existing words in the array at position >= numWords should be zero.
- Method Detail
  - iterator
```
public DocIdSetIterator iterator()
```
    Description copied from class: DocIdSet
    
    Provides a DocIdSetIterator to access the set. This implementation can return null if there are no docs that match.
    
    Specified by:
    
    iterator in class DocIdSet
  - bits
```
public Bits bits()
```
    Description copied from class: DocIdSet
    
    Optionally provides a Bits interface for random access to matching documents.
    
    Overrides:
    
    bits in class DocIdSet
    
    Returns:
    
    null, if this DocIdSet does not support random access. In contrast to DocIdSet.iterator(), a return value of null does not imply that no documents match the filter! The default implementation does not provide random access, so you only need to implement this method if your DocIdSet can guarantee random access to every docid in O(1) time without external disk access (as Bits interface cannot throw IOException). This is generally true for bit sets like FixedBitSet, which return itself if they are used as DocIdSet.
  - isCacheable
```
public boolean isCacheable()
```
    This DocIdSet implementation is cacheable.
    
    Overrides:
    
    isCacheable in class DocIdSet
  - capacity
```
public long capacity()
```
    Returns the current capacity in bits (1 greater than the index of the last bit)
  - size
```
public long size()
```
    Returns the current capacity of this set. Included for compatibility. This is *not* equal to cardinality()
  - length
```
public int length()
```
    Description copied from interface: Bits
    
    Returns the number of bits in this set
    
    Specified by:
    
    length in interface Bits
  - isEmpty
```
public boolean isEmpty()
```
    Returns true if there are no set bits
  - getBits
```
public long[] getBits()
```
    Expert: returns the long[] storing the bits
  - getNumWords
```
public int getNumWords()
```
    Expert: gets the number of longs in the array that are in use
  - get
```
public boolean get(int index)
```
    Returns true or false for the specified bit index.
    
    Specified by:
    
    get in interface Bits
    
    Parameters:
    
    index - index, should be non-negative and < Bits.length(). The result of passing negative or out of bounds values is undefined by this interface, just don't do it!
    
    Returns:
    
    true if the bit is set, false otherwise.
  - fastGet
```
public boolean fastGet(int index)
```
    Returns true or false for the specified bit index. The index should be less than the OpenBitSet size
  - get
```
public boolean get(long index)
```
    Returns true or false for the specified bit index
  - fastGet
```
public boolean fastGet(long index)
```
    Returns true or false for the specified bit index. The index should be less than the OpenBitSet size.
  - getBit
```
public int getBit(int index)
```
    returns 1 if the bit is set, 0 if not. The index should be less than the OpenBitSet size
  - set
```
public void set(long index)
```
    sets a bit, expanding the set size if necessary
  - fastSet
```
public void fastSet(int index)
```
    Sets the bit at the specified index. The index should be less than the OpenBitSet size.
  - fastSet
```
public void fastSet(long index)
```
    Sets the bit at the specified index. The index should be less than the OpenBitSet size.
  - set
```
public void set(long startIndex,
                long endIndex)
```
    Sets a range of bits, expanding the set size if necessary
    
    Parameters:
    
    startIndex - lower index
    
    endIndex - one-past the last bit to set
  - expandingWordNum
```
protected int expandingWordNum(long index)
```
  - fastClear
```
public void fastClear(int index)
```
    clears a bit. The index should be less than the OpenBitSet size.
  - fastClear
```
public void fastClear(long index)
```
    clears a bit. The index should be less than the OpenBitSet size.
  - clear
```
public void clear(long index)
```
    clears a bit, allowing access beyond the current set size without changing the size.
  - clear
```
public void clear(int startIndex,
                  int endIndex)
```
    Clears a range of bits. Clearing past the end does not change the size of the set.
    
    Parameters:
    
    startIndex - lower index
    
    endIndex - one-past the last bit to clear
  - clear
```
public void clear(long startIndex,
                  long endIndex)
```
    Clears a range of bits. Clearing past the end does not change the size of the set.
    
    Parameters:
    
    startIndex - lower index
    
    endIndex - one-past the last bit to clear
  - getAndSet
```
public boolean getAndSet(int index)
```
    Sets a bit and returns the previous value. The index should be less than the OpenBitSet size.
  - getAndSet
```
public boolean getAndSet(long index)
```
    Sets a bit and returns the previous value. The index should be less than the OpenBitSet size.
  - fastFlip
```
public void fastFlip(int index)
```
    flips a bit. The index should be less than the OpenBitSet size.
  - fastFlip
```
public void fastFlip(long index)
```
    flips a bit. The index should be less than the OpenBitSet size.
  - flip
```
public void flip(long index)
```
    flips a bit, expanding the set size if necessary
  - flipAndGet
```
public boolean flipAndGet(int index)
```
    flips a bit and returns the resulting bit value. The index should be less than the OpenBitSet size.
  - flipAndGet
```
public boolean flipAndGet(long index)
```
    flips a bit and returns the resulting bit value. The index should be less than the OpenBitSet size.
  - flip
```
public void flip(long startIndex,
                 long endIndex)
```
    Flips a range of bits, expanding the set size if necessary
    
    Parameters:
    
    startIndex - lower index
    
    endIndex - one-past the last bit to flip
  - cardinality
```
public long cardinality()
```
    Returns:
    
    the number of set bits
  - intersectionCount
```
public static long intersectionCount(OpenBitSet a,
                                     OpenBitSet b)
```
    Returns the popcount or cardinality of the intersection of the two sets. Neither set is modified.
  - unionCount
```
public static long unionCount(OpenBitSet a,
                              OpenBitSet b)
```
    Returns the popcount or cardinality of the union of the two sets. Neither set is modified.
  - andNotCount
```
public static long andNotCount(OpenBitSet a,
                               OpenBitSet b)
```
    Returns the popcount or cardinality of "a and not b" or "intersection(a, not(b))". Neither set is modified.
  - xorCount
```
public static long xorCount(OpenBitSet a,
                            OpenBitSet b)
```
    Returns the popcount or cardinality of the exclusive-or of the two sets. Neither set is modified.
  - nextSetBit
```
public int nextSetBit(int index)
```
    Returns the index of the first set bit starting at the index specified. -1 is returned if there are no more set bits.
  - nextSetBit
```
public long nextSetBit(long index)
```
    Returns the index of the first set bit starting at the index specified. -1 is returned if there are no more set bits.
  - prevSetBit
```
public int prevSetBit(int index)
```
    Returns the index of the first set bit starting downwards at the index specified. -1 is returned if there are no more set bits.
  - prevSetBit
```
public long prevSetBit(long index)
```
    Returns the index of the first set bit starting downwards at the index specified. -1 is returned if there are no more set bits.
  - clone
```
public OpenBitSet clone()
```
    Overrides:
    
    clone in class Object
  - intersect
```
public void intersect(OpenBitSet other)
```
    this = this AND other
  - union
```
public void union(OpenBitSet other)
```
    this = this OR other
  - remove
```
public void remove(OpenBitSet other)
```
    Remove all elements set in other. this = this AND_NOT other
  - xor
```
public void xor(OpenBitSet other)
```
    this = this XOR other
  - and
```
public void and(OpenBitSet other)
```
  - or
```
public void or(OpenBitSet other)
```
  - andNot
```
public void andNot(OpenBitSet other)
```
  - intersects
```
public boolean intersects(OpenBitSet other)
```
    returns true if the sets have any elements in common
  - ensureCapacityWords
```
public void ensureCapacityWords(int numWords)
```
    Expand the long[] with the size given as a number of words (64 bit longs).
  - ensureCapacity
```
public void ensureCapacity(long numBits)
```
    Ensure that the long[] is big enough to hold numBits, expanding it if necessary.
  - trimTrailingZeros
```
public void trimTrailingZeros()
```
    Lowers numWords, the number of words in use, by checking for trailing zero words.
  - bits2words
```
public static int bits2words(long numBits)
```
    returns the number of 64 bit words it would take to hold numBits
  - equals
```
public boolean equals(Object o)
```
    returns true if both sets have the same bits set
    
    Overrides:
    
    equals in class Object
  - hashCode
```
public int hashCode()
```
    Overrides:
    
    hashCode in class Object

	cardinality	intersect_count	union	nextSetBit	get	iterator
50% full	3.36	3.96	1.44	1.46	1.99	1.58
1% full	3.31	3.90		1.04		0.99

	cardinality	intersect_count	union	nextSetBit	get	iterator
50% full	2.50	3.50	1.00	1.03	1.12	1.25
1% full	2.51	3.49		1.00		1.02

Class OpenBitSet

Performance Results

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.lucene.util.Bits

Field Summary

Fields inherited from interface org.apache.lucene.util.Bits

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

bits

wlen

Constructor Detail

OpenBitSet

OpenBitSet

OpenBitSet

Method Detail

iterator

bits

isCacheable

capacity

size

length

isEmpty

getBits

getNumWords

get

fastGet

get

fastGet

getBit

set

fastSet

fastSet

set

expandingWordNum

fastClear

fastClear

clear

clear

clear

getAndSet

getAndSet

fastFlip

fastFlip

flip

flipAndGet

flipAndGet

flip

cardinality

intersectionCount

unionCount

andNotCount

xorCount

nextSetBit

nextSetBit

prevSetBit

prevSetBit

clone

intersect

union

remove

xor

and

or

andNot

intersects

ensureCapacityWords

ensureCapacity

trimTrailingZeros

bits2words

equals

hashCode