java.util

Class BitSet

public class BitSet extends Object implements Cloneable, Serializable

This class can be thought of in two ways. You can see it as a vector of bits or as a set of non-negative integers. The name BitSet is a bit misleading. It is implemented by a bit vector, but its equally possible to see it as set of non-negative integer; each integer in the set is represented by a set bit at the corresponding index. The size of this structure is determined by the highest integer in the set. You can union, intersect and build (symmetric) remainders, by invoking the logical operations and, or, andNot, resp. xor. This implementation is NOT synchronized against concurrent access from multiple threads. Specifically, if one thread is reading from a bitset while another thread is simultaneously modifying it, the results are undefined.

UNKNOWN: updated to 1.4

Constructor Summary
	BitSet() Create a new empty bit set.
	BitSet(int nbits) Create a new empty bit set, with a given size.

Method Summary
void	and(BitSet bs) Performs the logical AND operation on this bit set and the given `set`.
void	andNot(BitSet bs) Performs the logical AND operation on this bit set and the complement of the given `bs`.
int	cardinality() Returns the number of bits set to true.
void	clear() Sets all bits in the set to false.
void	clear(int pos) Removes the integer `pos` from this set.
void	clear(int from, int to) Sets the bits between from (inclusive) and to (exclusive) to false.
Object	clone() Create a clone of this bit set, that is an instance of the same class and contains the same elements.
boolean	equals(Object obj) Returns true if the `obj` is a bit set that contains exactly the same elements as this bit set, otherwise false.
void	flip(int index) Sets the bit at the index to the opposite value.
void	flip(int from, int to) Sets a range of bits to the opposite value.
boolean	get(int pos) Returns true if the integer `bitIndex` is in this bit set, otherwise false.
BitSet	get(int from, int to) Returns a new `BitSet` composed of a range of bits from this one.
int	hashCode() Returns a hash code value for this bit set.
boolean	intersects(BitSet set) Returns true if the specified BitSet and this one share at least one common true bit.
boolean	isEmpty() Returns true if this set contains no true bits.
int	length() Returns the logical number of bits actually used by this bit set.
int	nextClearBit(int from) Returns the index of the next false bit, from the specified bit (inclusive).
int	nextSetBit(int from) Returns the index of the next true bit, from the specified bit (inclusive).
void	or(BitSet bs) Performs the logical OR operation on this bit set and the given `set`.
void	set(int pos) Add the integer `bitIndex` to this set.
void	set(int index, boolean value) Sets the bit at the given index to the specified value.
void	set(int from, int to) Sets the bits between from (inclusive) and to (exclusive) to true.
void	set(int from, int to, boolean value) Sets the bits between from (inclusive) and to (exclusive) to the specified value.
int	size() Returns the number of bits actually used by this bit set.
String	toString() Returns the string representation of this bit set.
void	xor(BitSet bs) Performs the logical XOR operation on this bit set and the given `set`.

Constructor Detail

BitSet

public BitSet()

Create a new empty bit set. All bits are initially false.

BitSet

public BitSet(int nbits)

Create a new empty bit set, with a given size. This constructor reserves enough space to represent the integers from 0 to nbits-1.

Parameters: nbits the initial size of the bit set

Throws: NegativeArraySizeException if nbits < 0

Method Detail

and

public void and(BitSet bs)

Performs the logical AND operation on this bit set and the given set. This means it builds the intersection of the two sets. The result is stored into this bit set.

Parameters: bs the second bit set

Throws: NullPointerException if bs is null

andNot

public void andNot(BitSet bs)

Performs the logical AND operation on this bit set and the complement of the given bs. This means it selects every element in the first set, that isn't in the second set. The result is stored into this bit set and is effectively the set difference of the two.

Parameters: bs the second bit set

Throws: NullPointerException if bs is null

Since: 1.2

cardinality

public int cardinality()

Returns the number of bits set to true.

Returns: the number of true bits

Since: 1.4

clear

public void clear()

Sets all bits in the set to false.

Since: 1.4

clear

public void clear(int pos)

Removes the integer pos from this set. That is the corresponding bit is cleared. If the index is not in the set, this method does nothing.

Parameters: pos a non-negative integer

Throws: IndexOutOfBoundsException if pos < 0

clear

public void clear(int from, int to)

Sets the bits between from (inclusive) and to (exclusive) to false.

Parameters: from the start range (inclusive) to the end range (exclusive)

Throws: IndexOutOfBoundsException if from < 0 || to < 0 || from > to

Since: 1.4

clone

public Object clone()

Create a clone of this bit set, that is an instance of the same class and contains the same elements. But it doesn't change when this bit set changes.

Returns: the clone of this object.

equals

public boolean equals(Object obj)

Returns true if the obj is a bit set that contains exactly the same elements as this bit set, otherwise false.

Parameters: obj the object to compare to

Returns: true if obj equals this bit set

flip

public void flip(int index)

Sets the bit at the index to the opposite value.

Parameters: index the index of the bit

Throws: IndexOutOfBoundsException if index is negative

Since: 1.4

flip

public void flip(int from, int to)

Sets a range of bits to the opposite value.

Parameters: from the low index (inclusive) to the high index (exclusive)

Throws: IndexOutOfBoundsException if from > to || from < 0 || to < 0

Since: 1.4

get

public boolean get(int pos)

Returns true if the integer bitIndex is in this bit set, otherwise false.

Parameters: pos a non-negative integer

Returns: the value of the bit at the specified position

Throws: IndexOutOfBoundsException if the pos is negative

get

public BitSet get(int from, int to)

Returns a new BitSet composed of a range of bits from this one.

Parameters: from the low index (inclusive) to the high index (exclusive)

Throws: IndexOutOfBoundsException if from > to || from < 0 || to < 0

Since: 1.4

hashCode

public int hashCode()

Returns a hash code value for this bit set. The hash code of two bit sets containing the same integers is identical. The algorithm used to compute it is as follows: Suppose the bits in the BitSet were to be stored in an array of long integers called bits, in such a manner that bit k is set in the BitSet (for non-negative values of k) if and only if

((k/64) < bits.length)
 && ((bits[k/64] & (1L << (bit % 64))) != 0)

Then the following definition of the hashCode method would be a correct implementation of the actual algorithm:

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

  return (int)((h >> 32) ^ h);
}

Note that the hash code values changes, if the set is changed.

Returns: the hash code value for this bit set.

intersects

public boolean intersects(BitSet set)

Returns true if the specified BitSet and this one share at least one common true bit.

Parameters: set the set to check for intersection

Returns: true if the sets intersect

Throws: NullPointerException if set is null

Since: 1.4

isEmpty

public boolean isEmpty()

Returns true if this set contains no true bits.

Returns: true if all bits are false

Since: 1.4

length

public int length()

Returns the logical number of bits actually used by this bit set. It returns the index of the highest set bit plus one. Note that this method doesn't return the number of set bits.

Returns: the index of the highest set bit plus one.

nextClearBit

public int nextClearBit(int from)

Returns the index of the next false bit, from the specified bit (inclusive).

Parameters: from the start location

Returns: the first false bit

Throws: IndexOutOfBoundsException if from is negative

Since: 1.4

nextSetBit

public int nextSetBit(int from)

Returns the index of the next true bit, from the specified bit (inclusive). If there is none, -1 is returned. You can iterate over all true bits with this loop:

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

Parameters: from the start location

Returns: the first true bit, or -1

Throws: IndexOutOfBoundsException if from is negative

Since: 1.4

or

public void or(BitSet bs)

Performs the logical OR operation on this bit set and the given set. This means it builds the union of the two sets. The result is stored into this bit set, which grows as necessary.

Parameters: bs the second bit set

Throws: NullPointerException if bs is null

set

public void set(int pos)

Add the integer bitIndex to this set. That is the corresponding bit is set to true. If the index was already in the set, this method does nothing. The size of this structure is automatically increased as necessary.

Parameters: pos a non-negative integer.

Throws: IndexOutOfBoundsException if pos is negative

set

public void set(int index, boolean value)

Sets the bit at the given index to the specified value. The size of this structure is automatically increased as necessary.

Parameters: index the position to set value the value to set it to

Throws: IndexOutOfBoundsException if index is negative

Since: 1.4

set

public void set(int from, int to)

Sets the bits between from (inclusive) and to (exclusive) to true.

Parameters: from the start range (inclusive) to the end range (exclusive)

Throws: IndexOutOfBoundsException if from < 0 || from > to || to < 0

Since: 1.4

set

public void set(int from, int to, boolean value)

Sets the bits between from (inclusive) and to (exclusive) to the specified value.

Parameters: from the start range (inclusive) to the end range (exclusive) value the value to set it to

Throws: IndexOutOfBoundsException if from < 0 || from > to || to < 0

Since: 1.4

size

public int size()

Returns the number of bits actually used by this bit set. Note that this method doesn't return the number of set bits, and that future requests for larger bits will make this automatically grow.

Returns: the number of bits currently used.

toString

public String toString()

Returns the string representation of this bit set. This consists of a comma separated list of the integers in this set surrounded by curly braces. There is a space after each comma. A sample string is thus "{1, 3, 53}".

Returns: the string representation.

xor

public void xor(BitSet bs)

Performs the logical XOR operation on this bit set and the given set. This means it builds the symmetric remainder of the two sets (the elements that are in one set, but not in the other). The result is stored into this bit set, which grows as necessary.

Parameters: bs the second bit set

Throws: NullPointerException if bs is null