Class BitSet

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.

Constructors

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

Methods

valueOf

public static BitSet valueOf(long[] 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

Since:

1.7

valueOf

public static BitSet valueOf(LongBuffer lb)

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

Since:

1.7

valueOf

public static BitSet valueOf(byte[] 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

Since:

1.7

valueOf

public static BitSet valueOf(ByteBuffer bb)

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

Since:

1.7

toByteArray

public byte[] toByteArray()

Returns:

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

Since:

1.7

toLongArray

public long[] toLongArray()

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)

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

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)

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()

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);
 }

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)

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()

BitSet drPepper = new BitSet();

drPepper.set(2);

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

Overrides:

toString in class Object

Returns:

a string representation of this bit set

stream

public IntStream stream()

Returns:

a stream of integers representing set indices

Since:

1.8