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.

Since:

JDK1.0

See Also:

Serialized Form

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.
void	clear(int bitIndex) Sets the bit specified by the index 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.
boolean	get(int bitIndex) Returns the value of the bit with the specified index.
int	hashCode() Returns a hash code value for this bit set.
int	length() Returns the "logical size" of this BitSet: the index of the highest set bit in the BitSet plus one.
void	or(BitSet set) Performs a logical OR of this bit set with the bit set argument.
void	set(int bitIndex) Sets the bit specified by the index to true.
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.
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

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

set

public void set(int bitIndex)

Sets the bit specified by the index to true.

Parameters:

bitIndex - a bit index.

Throws:

IndexOutOfBoundsException - if the specified index is negative.

Since:

JDK1.0

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

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

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.

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.

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 synchronized 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.

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()

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 indeces aer listed in order from lowest to highest, separated by ",$nbsp;" (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.