java.util
Class BitSet

java.lang.Object
  java.util.BitSet

All Implemented Interfaces:

Cloneable, Serializable

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.

Since:

JDK1.0

Author:

Arthur van Hoff, Michael McCloskey

See Also:

Serialized Form

Field Summary

private static int	ADDRESS_BITS_PER_UNIT
private static int	BIT_INDEX_MASK
private long[]	bits The bits in this BitSet.
private static int	BITS_PER_UNIT
private static long	serialVersionUID
private static byte[]	trailingZeroTable
private int	unitsInUse The number of units in the logical size of this BitSet.
private static long	WORD_MASK

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.

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.
private static long	bit(int bitIndex) Given a bit index, return a unit that masks that bit in its unit.
private static int	bitCount(long val) Returns the number of bits set in val.
private static int	bitLen(int w) bitLen(val) is the number of bits in val.
private static long	bitsLeftOf(int x) Returns a long that has all the bits that are more significant than or equal to the specified index set to 1.
private static long	bitsRightOf(int x) Returns a long that has all bits that are less significant than the specified index set to 1.
int	cardinality() Returns the number of bits set to true in this BitSet.
void	clear() Sets all of the bits in this BitSet to false.
void	clear(int bitIndex) Sets the bit specified by the index to false.
void	clear(int fromIndex, int toIndex) Sets the bits from the specified fromIndex(inclusive) to the specified toIndex(exclusive) to false.
Object	clone() Cloning this BitSet produces a new BitSet that is equal to it.
private void	ensureCapacity(int unitsRequired) Ensures that the BitSet can hold enough units.
boolean	equals(Object obj) Compares this object against the specified object.
void	flip(int bitIndex) Sets the bit at the specified index to 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).
private long	getBits(int j) Returns the unit of this bitset at index j as if this bitset had an infinite amount of storage.
int	hashCode() Returns a 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.
private void	readObject(ObjectInputStream in) This override of readObject makes sure unitsInUse is set properly when deserializing a bitset
private void	recalculateUnitsInUse() Set the field unitsInUse with the logical size in units of the bit set.
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.
void	set(int fromIndex, int toIndex) Sets the bits from the specified fromIndex(inclusive) to the specified toIndex(exclusive) to true.
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.
int	size() Returns the number of bits of space actually in use by this BitSet to represent bit values.
String	toString() Returns a string representation of this bit set.
private static int	trailingZeroCnt(long val)
private static int	unitIndex(int bitIndex) Given a bit index return unit index containing it.
void	xor(BitSet set) Performs a logical XOR of this bit set with the bit set argument.

Methods inherited from class java.lang.Object

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

Field Detail

ADDRESS_BITS_PER_UNIT

private static final int ADDRESS_BITS_PER_UNIT

See Also:

Constant Field Values

BITS_PER_UNIT

private static final int BITS_PER_UNIT

See Also:

Constant Field Values

BIT_INDEX_MASK

private static final int BIT_INDEX_MASK

See Also:

Constant Field Values

WORD_MASK

private static final long WORD_MASK

See Also:

Constant Field Values

bits

private long[] bits

The bits in this BitSet. The ith bit is stored in bits[i/64] at bit position i % 64 (where bit position 0 refers to the least significant bit and 63 refers to the most significant bit). INVARIANT: The words in bits[] above unitInUse-1 are zero.

unitsInUse

private transient int unitsInUse

The number of units in the logical size of this BitSet. INVARIANT: unitsInUse is nonnegative. INVARIANT: bits[unitsInUse-1] is nonzero unless unitsInUse is zero.

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

trailingZeroTable

private static final byte[] trailingZeroTable

Constructor Detail

BitSet

public BitSet()

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

BitSet

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.

Method Detail

unitIndex

private static int unitIndex(int bitIndex)

Given a bit index return unit index containing it.

bit

private static long bit(int bitIndex)

Given a bit index, return a unit that masks that bit in its unit.

recalculateUnitsInUse

private void recalculateUnitsInUse()

Set the field unitsInUse with the logical size in units of the bit set. WARNING:This function assumes that the number of units actually in use is less than or equal to the current value of unitsInUse!

ensureCapacity

private void ensureCapacity(int unitsRequired)

Ensures that the BitSet can hold enough units.

Parameters:

unitsRequired - the minimum acceptable number of units.

flip

public void flip(int bitIndex)

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

Parameters:

bitIndex - the index of the bit to flip.

Throws:

IndexOutOfBoundsException - if the specified index is negative.

Since:

1.4

flip

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.

Since:

1.4

bitsRightOf

private static long bitsRightOf(int x)

Returns a long that has all bits that are less significant than the specified index set to 1. All other bits are 0.

bitsLeftOf

private static long bitsLeftOf(int x)

Returns a long that has all the bits that are more significant than or equal to the specified index set to 1. All other bits are 0.

set

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.

Since:

JDK1.0

set

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.

Since:

1.4

set

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.

Since:

1.4

set

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.

Since:

1.4

clear

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.

Since:

JDK1.0

clear

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.

Since:

1.4

clear

public void clear()

Sets all of the bits in this BitSet to false.

Since:

1.4

get

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.

get

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.

Since:

1.4

getBits

private long getBits(int j)

Returns the unit of this bitset at index j as if this bitset had an infinite amount of storage.

nextSetBit

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 }

Parameters:

fromIndex - the index to start checking from (inclusive).

Returns:

the index of the next set bit.

Throws:

IndexOutOfBoundsException - if the specified index is negative.

Since:

1.4

trailingZeroCnt

private static int trailingZeroCnt(long val)

nextClearBit

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.

Since:

1.4

length

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.

Since:

1.2

bitLen

private static int bitLen(int w)

bitLen(val) is the number of bits in val.

isEmpty

public boolean isEmpty()

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

Returns:

boolean indicating whether this BitSet is empty.

Since:

1.4

intersects

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.

Since:

1.4

cardinality

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.

Since:

1.4

bitCount

private static int bitCount(long val)

Returns the number of bits set in val. For a derivation of this algorithm, see "Algorithms and data structures with applications to graphics and geometry", by Jurg Nievergelt and Klaus Hinrichs, Prentice Hall, 1993.

and

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.

or

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.

xor

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.

andNot

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.

Since:

JDK1.2

hashCode

public int hashCode()

Returns a hash code value for this bit set. The has code depends only on which bits have been set within this BitSet. The algorithm used to compute it may be described as follows.

Suppose the bits in the BitSet were to be stored in an array of long integers called, say, bits, in such a manner that bit k is set in the BitSet (for nonnegative values of k) if and only if the expression

((k>>6) < bits.length) && ((bits[k>>6] & (1L << (bit & 0x3F))) != 0)

is true. 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; --i >= 0; ) {
           h ^= bits[i] * (i + 1);
      }
      return (int)((h >> 32) ^ h);
 }

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

Overrides the hashCode method of Object.

Overrides:

hashCode in class Object

Returns:

a hash code value for this bit set.

See Also:

Object.equals(java.lang.Object), Hashtable

size

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.

equals

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.

Overrides the equals method of Object.

Overrides:

equals in class Object

Parameters:

obj - the object to compare with.

Returns:

true if the objects are the same; false otherwise.

See Also:

size()

clone

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 and the same current size.

Overrides the clone method of Object.

Overrides:

clone in class Object

Returns:

a clone of this bit set.

See Also:

size()

readObject

private void readObject(ObjectInputStream in)
                 throws IOException,
                        ClassNotFoundException

This override of readObject makes sure unitsInUse is set properly when deserializing a bitset

Throws:

IOException

ClassNotFoundException

toString

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.

Overrides the toString method of Object.

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}".

Overrides:

toString in class Object

Returns:

a string representation of this bit set.