java.util

Class BitSet

java.lang.Object

java.util.BitSet

All Implemented Interfaces:

Serializable, Cloneable

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, Martin Buchholz

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
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

Methods

Modifier and Type	Method and Description
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() 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.
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 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.
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.
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

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

valueOf

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

Since:

1.7

toLongArray

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

Since:

1.7

flip

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

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

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

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, or -1 if there is no such bit

Throws:

IndexOutOfBoundsException - if the specified index is negative

Since:

1.4

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

previousSetBit

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

Since:

1.7

previousClearBit

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

Since:

1.7

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

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

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:

1.2

hashCode

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.

Overrides:

hashCode in class Object

Returns:

the hash code value for this bit set

See Also:

Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

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:

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.

Overrides:

clone in class Object

Returns:

a clone of this bit set

See Also:

size()

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.

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