BitSet

public class BitSet extends Object
implements Cloneable Serializable

This class implements a vector of bits that grows as needed. Each component of the bit set has a boolean value. The bits of a BitSet are indexed by nonnegative integers. Individual indexed bits can be examined, set, or cleared. One BitSet may be used to modify the contents of another BitSet through logical AND, logical inclusive OR, and logical exclusive OR operations.

By default, all bits in the set initially have the value false.

Every bit set has a current size, which is the number of bits of space currently in use by the bit set. Note that the size is related to the implementation of a bit set, so it may change with implementation. The length of a bit set relates to logical length of a bit set and is defined independently of implementation.

Unless otherwise noted, passing a null parameter to any of the methods in a BitSet will result in a NullPointerException.

A BitSet is not safe for multithreaded use without external synchronization.

Public Constructor Summary

	BitSet() Creates a new bit set.
	BitSet(int nbits) Creates a bit set whose initial size is large enough to explicitly represent bits with indices in the range 0 through nbits-1.

Public Method Summary

void	and(BitSet set) Performs a logical AND of this target bit set with the argument bit set.
void	andNot(BitSet set) Clears all of the bits in this BitSet whose corresponding bit is set in the specified BitSet.
int	cardinality() Returns the number of bits set to true in this BitSet.
void	clear(int fromIndex, int toIndex) Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to false.
void	clear(int bitIndex) Sets the bit specified by the index to false.
void	clear() Sets all of the bits in this BitSet to false.
Object	clone() Cloning this BitSet produces a new BitSet that is equal to it.
boolean	equals(Object obj) Compares this object against the specified object.
void	flip(int bitIndex) Sets the bit at the specified index to the complement of its current value.
void	flip(int fromIndex, int toIndex) Sets each bit from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the complement of its current value.
boolean	get(int bitIndex) Returns the value of the bit with the specified index.
BitSet	get(int fromIndex, int toIndex) Returns a new BitSet composed of bits from this BitSet from fromIndex (inclusive) to toIndex (exclusive).
int	hashCode() Returns the hash code value for this bit set.
boolean	intersects(BitSet set) Returns true if the specified BitSet has any bits set to true that are also set to true in this BitSet.
boolean	isEmpty() Returns true if this BitSet contains no bits that are set to true.
int	length() Returns the "logical size" of this BitSet: the index of the highest set bit in the BitSet plus one.
int	nextClearBit(int fromIndex) Returns the index of the first bit that is set to false that occurs on or after the specified starting index.
int	nextSetBit(int fromIndex) Returns the index of the first bit that is set to true that occurs on or after the specified starting index.
void	or(BitSet set) Performs a logical OR of this bit set with the bit set argument.
int	previousClearBit(int fromIndex) Returns the index of the nearest bit that is set to false that occurs on or before the specified starting index.
int	previousSetBit(int fromIndex) Returns the index of the nearest bit that is set to true that occurs on or before the specified starting index.
void	set(int fromIndex, int toIndex, boolean value) Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the specified value.
void	set(int fromIndex, int toIndex) Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to true.
void	set(int bitIndex) Sets the bit at the specified index to true.
void	set(int bitIndex, boolean value) Sets the bit at the specified index to the specified value.
int	size() Returns the number of bits of space actually in use by this BitSet to represent bit values.
IntStream	stream() Returns a stream of indices for which this BitSet contains a bit in the set state.
byte[]	toByteArray() Returns a new byte array containing all the bits in this bit set.
long[]	toLongArray() Returns a new long array containing all the bits in this bit set.
String	toString() Returns a string representation of this bit set.
static BitSet	valueOf(long[] longs) Returns a new bit set containing all the bits in the given long array.
static BitSet	valueOf(byte[] bytes) Returns a new bit set containing all the bits in the given byte array.
static BitSet	valueOf(ByteBuffer bb) Returns a new bit set containing all the bits in the given byte buffer between its position and limit.
static BitSet	valueOf(LongBuffer lb) Returns a new bit set containing all the bits in the given long buffer between its position and limit.
void	xor(BitSet set) Performs a logical XOR of this bit set with the bit set argument.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public BitSet ()

Creates a new bit set. All bits are initially false.

public BitSet (int nbits)

Creates a bit set whose initial size is large enough to explicitly represent bits with indices in the range 0 through nbits-1. All bits are initially false.

Parameters

nbits	the initial size of the bit set

Throws

NegativeArraySizeException	if the specified initial size is negative

Public Methods

public void and (BitSet set)

Performs a logical AND of this target bit set with the argument bit set. This bit set is modified so that each bit in it has the value true if and only if it both initially had the value true and the corresponding bit in the bit set argument also had the value true.

Parameters

set	a bit set

public void andNot (BitSet set)

Clears all of the bits in this BitSet whose corresponding bit is set in the specified BitSet.

Parameters

set	the BitSet with which to mask this BitSet

public int cardinality ()

Returns the number of bits set to true in this BitSet.

Returns

• the number of bits set to true in this BitSet

public void clear (int fromIndex, int toIndex)

Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to false.

Parameters

fromIndex	index of the first bit to be cleared
toIndex	index after the last bit to be cleared

Throws

IndexOutOfBoundsException	if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex

public void clear (int bitIndex)

Sets the bit specified by the index to false.

Parameters

bitIndex	the index of the bit to be cleared

Throws

IndexOutOfBoundsException	if the specified index is negative

public void clear ()

Sets all of the bits in this BitSet to false.

public Object clone ()

Cloning this BitSet produces a new BitSet that is equal to it. The clone of the bit set is another bit set that has exactly the same bits set to true as this bit set.

Returns

• a clone of this bit set

See Also

• size()

public boolean equals (Object obj)

Compares this object against the specified object. The result is true if and only if the argument is not null and is a Bitset object that has exactly the same set of bits set to true as this bit set. That is, for every nonnegative int index k,

((BitSet)obj).get(k) == this.get(k)

must be true. The current sizes of the two bit sets are not compared.

Parameters

obj	the object to compare with

Returns

• true if the objects are the same; false otherwise

See Also

• size()

public void flip (int bitIndex)

Sets the bit at the specified index to the complement of its current value.

Parameters

bitIndex	the index of the bit to flip

Throws

IndexOutOfBoundsException	if the specified index is negative

public void flip (int fromIndex, int toIndex)

Sets each bit from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the complement of its current value.

Parameters

fromIndex	index of the first bit to flip
toIndex	index after the last bit to flip

Throws

IndexOutOfBoundsException	if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex

public boolean get (int bitIndex)

Returns the value of the bit with the specified index. The value is true if the bit with the index bitIndex is currently set in this BitSet; otherwise, the result is false.

Parameters

bitIndex	the bit index

Returns

• the value of the bit with the specified index

Throws

IndexOutOfBoundsException	if the specified index is negative

public BitSet get (int fromIndex, int toIndex)

Returns a new BitSet composed of bits from this BitSet from fromIndex (inclusive) to toIndex (exclusive).

Parameters

fromIndex	index of the first bit to include
toIndex	index after the last bit to include

Returns

• a new BitSet from a range of this BitSet

Throws

IndexOutOfBoundsException	if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex

public int hashCode ()

Returns the hash code value for this bit set. The hash code depends only on which bits are set within this BitSet.

The hash code is defined to be the result of the following calculation:

 public int hashCode() {
     long h = 1234;
     long[] words = toLongArray();
     for (int i = words.length; --i >= 0; )
         h ^= words[i] * (i + 1);
     return (int)((h >> 32) ^ h);
 }

Note that the hash code changes if the set of bits is altered.

Returns

• the hash code value for this bit set

public boolean intersects (BitSet set)

Returns true if the specified BitSet has any bits set to true that are also set to true in this BitSet.

Parameters

set	BitSet to intersect with

Returns

• boolean indicating whether this BitSet intersects the specified BitSet

public boolean isEmpty ()

Returns true if this BitSet contains no bits that are set to true.

Returns

• boolean indicating whether this BitSet is empty

public int length ()

Returns the "logical size" of this BitSet: the index of the highest set bit in the BitSet plus one. Returns zero if the BitSet contains no set bits.

Returns

• the logical size of this BitSet

public int nextClearBit (int fromIndex)

Returns the index of the first bit that is set to false that occurs on or after the specified starting index.

Parameters

fromIndex	the index to start checking from (inclusive)

Returns

• the index of the next clear bit

Throws

IndexOutOfBoundsException	if the specified index is negative

public int nextSetBit (int fromIndex)

Returns the index of the first bit that is set to true that occurs on or after the specified starting index. If no such bit exists then -1 is returned.

To iterate over the true bits in a BitSet, use the following loop:

 for (int i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i+1)) {
     // operate on index i here
     if (i == Integer.MAX_VALUE) {
         break; // or (i+1) would overflow
     }
 }

Parameters

fromIndex	the index to start checking from (inclusive)

Returns

• the index of the next set bit, or -1 if there is no such bit

Throws

IndexOutOfBoundsException	if the specified index is negative

public void or (BitSet set)

Performs a logical OR of this bit set with the bit set argument. This bit set is modified so that a bit in it has the value true if and only if it either already had the value true or the corresponding bit in the bit set argument has the value true.

Parameters

set	a bit set

public int previousClearBit (int fromIndex)

Returns the index of the nearest bit that is set to false that occurs on or before the specified starting index. If no such bit exists, or if -1 is given as the starting index, then -1 is returned.

Parameters

fromIndex	the index to start checking from (inclusive)

Returns

• the index of the previous clear bit, or -1 if there is no such bit

Throws

IndexOutOfBoundsException	if the specified index is less than -1

public int previousSetBit (int fromIndex)

Returns the index of the nearest bit that is set to true that occurs on or before the specified starting index. If no such bit exists, or if -1 is given as the starting index, then -1 is returned.

To iterate over the true bits in a BitSet, use the following loop:

 for (int i = bs.length(); (i = bs.previousSetBit(i-1)) >= 0; ) {
     // operate on index i here
 }

Parameters

fromIndex	the index to start checking from (inclusive)

Returns

• the index of the previous set bit, or -1 if there is no such bit

Throws

IndexOutOfBoundsException	if the specified index is less than -1

public void set (int fromIndex, int toIndex, boolean value)

Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the specified value.

Parameters

fromIndex	index of the first bit to be set
toIndex	index after the last bit to be set
value	value to set the selected bits to

Throws

IndexOutOfBoundsException	if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex

public void set (int fromIndex, int toIndex)

Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to true.

Parameters

fromIndex	index of the first bit to be set
toIndex	index after the last bit to be set

Throws

IndexOutOfBoundsException	if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex

public void set (int bitIndex)

Sets the bit at the specified index to true.

Parameters

bitIndex	a bit index

Throws

IndexOutOfBoundsException	if the specified index is negative

public void set (int bitIndex, boolean value)

Sets the bit at the specified index to the specified value.

Parameters

bitIndex	a bit index
value	a boolean value to set

Throws

IndexOutOfBoundsException	if the specified index is negative

public int size ()

Returns the number of bits of space actually in use by this BitSet to represent bit values. The maximum element in the set is the size - 1st element.

Returns

• the number of bits currently in this bit set

public IntStream stream ()

Returns a stream of indices for which this BitSet contains a bit in the set state. The indices are returned in order, from lowest to highest. The size of the stream is the number of bits in the set state, equal to the value returned by the cardinality() method.

The bit set must remain constant during the execution of the terminal stream operation. Otherwise, the result of the terminal stream operation is undefined.

Returns

• a stream of integers representing set indices

public byte[] toByteArray ()

Returns a new byte array containing all the bits in this bit set.

More precisely, if
byte[] bytes = s.toByteArray();
then bytes.length == (s.length()+7)/8 and
s.get(n) == ((bytes[n/8] & (1<<(n%8))) != 0)
for all n < 8 * bytes.length.

Returns

• a byte array containing a little-endian representation of all the bits in this bit set

public long[] toLongArray ()

Returns a new long array containing all the bits in this bit set.

More precisely, if
long[] longs = s.toLongArray();
then longs.length == (s.length()+63)/64 and
s.get(n) == ((longs[n/64] & (1L<<(n%64))) != 0)
for all n < 64 * longs.length.

Returns

• a long array containing a little-endian representation of all the bits in this bit set

public String toString ()

Returns a string representation of this bit set. For every index for which this BitSet contains a bit in the set state, the decimal representation of that index is included in the result. Such indices are listed in order from lowest to highest, separated by ", " (a comma and a space) and surrounded by braces, resulting in the usual mathematical notation for a set of integers.

Example:

 BitSet drPepper = new BitSet();

Now drPepper.toString() returns "{}".

 drPepper.set(2);

Now drPepper.toString() returns "{2}".

 drPepper.set(4);
 drPepper.set(10);

Now drPepper.toString() returns "{2, 4, 10}".

Returns

• a string representation of this bit set

public static BitSet valueOf (long[] longs)

Returns a new bit set containing all the bits in the given long array.

More precisely,
BitSet.valueOf(longs).get(n) == ((longs[n/64] & (1L<<(n%64))) != 0)
for all n < 64 * longs.length.

This method is equivalent to BitSet.valueOf(LongBuffer.wrap(longs)).

Parameters

longs	a long array containing a little-endian representation of a sequence of bits to be used as the initial bits of the new bit set

Returns

• a BitSet containing all the bits in the long array

public static BitSet valueOf (byte[] bytes)

Returns a new bit set containing all the bits in the given byte array.

More precisely,
BitSet.valueOf(bytes).get(n) == ((bytes[n/8] & (1<<(n%8))) != 0)
for all n < 8 * bytes.length.

This method is equivalent to BitSet.valueOf(ByteBuffer.wrap(bytes)).

Parameters

bytes	a byte array containing a little-endian representation of a sequence of bits to be used as the initial bits of the new bit set

Returns

• a BitSet containing all the bits in the byte array

public static BitSet valueOf (ByteBuffer bb)

Returns a new bit set containing all the bits in the given byte buffer between its position and limit.

More precisely,
BitSet.valueOf(bb).get(n) == ((bb.get(bb.position()+n/8) & (1<<(n%8))) != 0)
for all n < 8 * bb.remaining().

The byte buffer is not modified by this method, and no reference to the buffer is retained by the bit set.

Parameters

bb	a byte buffer containing a little-endian representation of a sequence of bits between its position and limit, to be used as the initial bits of the new bit set

Returns

• a BitSet containing all the bits in the buffer in the specified range

public static BitSet valueOf (LongBuffer lb)

Returns a new bit set containing all the bits in the given long buffer between its position and limit.

More precisely,
BitSet.valueOf(lb).get(n) == ((lb.get(lb.position()+n/64) & (1L<<(n%64))) != 0)
for all n < 64 * lb.remaining().

The long buffer is not modified by this method, and no reference to the buffer is retained by the bit set.

Parameters

lb	a long buffer containing a little-endian representation of a sequence of bits between its position and limit, to be used as the initial bits of the new bit set

Returns

• a BitSet containing all the bits in the buffer in the specified range

public void xor (BitSet set)

Performs a logical XOR of this bit set with the bit set argument. This bit set is modified so that a bit in it has the value true if and only if one of the following statements holds:

• The bit initially has the value true, and the corresponding bit in the argument has the value false.
• The bit initially has the value false, and the corresponding bit in the argument has the value true.

Parameters

set	a bit set