java.util.BitSet

public class java.util

BitSet

Java SE 6

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.

version 1.67, 04/07/06

since JDK1.0

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.

nbits	the initial size of the bit set.
Throws	NegativeArraySizeException: if the specified initial size is negative.

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.

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.

set	the `BitSet` with which to mask this `BitSet`.
since	1.2

public int

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

return	the number of bits set to `true` in this `BitSet`.
since	1.4

public void

clear(int bitIndex)
Sets the bit specified by the index to false.

bitIndex	the index of the bit to be cleared.
Throws	IndexOutOfBoundsException: if the specified index is negative.
since	JDK1.0

public void

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

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

public void

clear()
Sets all of the bits in this BitSet to false.

since

1.4

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 the clone method of Object.

return 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.

Overrides the equals method of Object.

obj the object to compare with.

return 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.

bitIndex	the index of the bit to flip.
Throws	IndexOutOfBoundsException: if the specified index is negative.
since	1.4

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.

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

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.

bitIndex	the bit index.
return	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).

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

public int

hashCode()
Returns a hash code value for this bit set. The hash 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, words, 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) < words.length) && ((words[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 = words.length; --i >= 0; ) {
           h ^= words[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.

return a 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.

set	`BitSet` to intersect with
return	boolean indicating whether this `BitSet` intersects the specified `BitSet`.
since	1.4

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.

return	the logical size of this `BitSet`.
since	1.2

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.

fromIndex	the index to start checking from (inclusive).
return	the index of the next clear bit.
Throws	IndexOutOfBoundsException: if the specified index is negative.
since	1.4

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
 }

fromIndex	the index to start checking from (inclusive).
return	the index of the next set bit.
Throws	IndexOutOfBoundsException: if the specified index is negative.
since	1.4

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.

set

a bit set.

public void

set(int bitIndex)
Sets the bit at the specified index to true.

bitIndex	a bit index.
Throws	IndexOutOfBoundsException: if the specified index is negative.
since	JDK1.0

public void

set(int bitIndex, boolean value)
Sets the bit at the specified index to the specified value.

bitIndex	a bit index.
value	a boolean value to set.
Throws	IndexOutOfBoundsException: if the specified index is negative.
since	1.4

public void

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

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

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.

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

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.

return

the number of bits currently 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.

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}".

return

a string representation of this bit set.

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.

set

a bit set.

Properties

public boolean

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

return	boolean indicating whether this `BitSet` is empty.
since	1.4

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Java SE 6

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