
[all packages] 
[package java.util] 
[class hierarchy] 
[index]

public final class java.util.BitSet

(source file: BitSet.java)

java.lang.Object
   |
   +----java.util.BitSet

The pure class interface.

public final class BitSet
  implements Cloneable, java.io.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 currently in the bit set.

BitSet(int): Creates a bit set whose initial size is the specified number of bits
BitSet(): Creates a new bit set

and(BitSet): Performs a logical AND of this target bit set with the argument bit set
clear(int): The bit with index bitIndex in this BitSet is changed to the
clone(): Cloning this BitSet produces a new BitSet that is equal to it.
equals(Object): Compares this object against the specified object. The result is true if and
get(int): Returns the value of the bit with the specified index
hashCode(): Returns a hash code value for this bit set
or(BitSet): Performs a logical OR of this bit set with the bit set argument
set(int): The bit with index bitIndex in this BitSet is changed to the
size(): Returns the number of bits of space actually in use by this BitSet to
toString(): Returns a string representation of this bit set
xor(BitSet): Performs a logical XOR of this bit set with the bit set argument

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 the specified number of bits. Enough space is reserved 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.

set

public void set(int bitIndex);

The bit with index bitIndex in this BitSet is changed to the "set" (true) state. If bitIndex is not smaller than the value that would be returned by the size method, then the size of this BitSet is increased to be larger than bitIndex.

Parameters:

bitIndex - a bit index.

Throws:

IndexOutOfBoundsException -if the specified index is negative.

clear

public void clear(int bitIndex);

The bit with index bitIndex in this BitSet is changed to the "clear" (false) state. If bitIndex is not smaller than the value that would be returned by the size method, then the size of this BitSet is increased to be larger than bitIndex.

Parameters:

bitIndex - the index of the bit to be cleared.

Throws:

IndexOutOfBoundsException -if the specified index is negative.

get

public boolean get(int bitIndex);

Returns the value of the bit with the specified index. The value is true if the bit iwth 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.

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.

Returns:

a hash code value for this bit set.

Overrides:

hashCode in class 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 the equals method of Object.

Parameters:

obj - the object to compare with.

Returns:

true if the objects are the same; false otherwise.

Overrides:

equals in class Object

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.

Returns:

a clone of this bit set.

Overrides:

clone in class Object

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}".

Returns:

a string representation of this bit set.

Overrides:

toString in class Object


[all packages] 
[package java.util] 
[class hierarchy] 
[index]

public final class java.util.BitSet

java.util.BitSet.html