
JSR 217 (Maintenance Release)  
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java.lang.Object java.util.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.
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
nbits1 . 
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 . 
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 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 a 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. 
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. 
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 
public BitSet()
false
.
public BitSet(int nbits)
0
through
nbits1
. All bits are initially false
.
nbits
 the initial size of the bit set.
NegativeArraySizeException
 if the specified initial size
is negative.Method Detail 
public void flip(int bitIndex)
bitIndex
 the index of the bit to flip.
IndexOutOfBoundsException
 if the specified index is negative.public void flip(int fromIndex, int toIndex)
fromIndex
 index of the first bit to flip.toIndex
 index after the last bit to flip.
IndexOutOfBoundsException
 if fromIndex is negative,
or toIndex is negative, or fromIndex is
larger than toIndex.public void set(int bitIndex)
true
.
bitIndex
 a bit index.
IndexOutOfBoundsException
 if the specified index is negative.public void set(int bitIndex, boolean value)
bitIndex
 a bit index.value
 a boolean value to set.
IndexOutOfBoundsException
 if the specified index is negative.public void set(int fromIndex, int toIndex)
true
.
fromIndex
 index of the first bit to be set.toIndex
 index after the last bit to be set.
IndexOutOfBoundsException
 if fromIndex is negative,
or toIndex is negative, or fromIndex is
larger than toIndex.public void set(int fromIndex, int toIndex, boolean value)
fromIndex
 index of the first bit to be set.toIndex
 index after the last bit to be setvalue
 value to set the selected bits to
IndexOutOfBoundsException
 if fromIndex is negative,
or toIndex is negative, or fromIndex is
larger than toIndex.public void clear(int bitIndex)
false
.
bitIndex
 the index of the bit to be cleared.
IndexOutOfBoundsException
 if the specified index is negative.public void clear(int fromIndex, int toIndex)
false
.
fromIndex
 index of the first bit to be cleared.toIndex
 index after the last bit to be cleared.
IndexOutOfBoundsException
 if fromIndex is negative,
or toIndex is negative, or fromIndex is
larger than toIndex.public void clear()
false
.
public boolean get(int bitIndex)
true
if the bit with the index bitIndex
is currently set in this BitSet
; otherwise, the result
is false
.
bitIndex
 the bit index.
IndexOutOfBoundsException
 if the specified index is negative.public BitSet get(int fromIndex, int toIndex)
fromIndex
 index of the first bit to include.toIndex
 index after the last bit to include.
IndexOutOfBoundsException
 if fromIndex is negative,
or toIndex is negative, or fromIndex is
larger than toIndex.public int nextSetBit(int fromIndex)
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).
IndexOutOfBoundsException
 if the specified index is negative.public int nextClearBit(int fromIndex)
false
that occurs on or after the specified starting index.
fromIndex
 the index to start checking from (inclusive).
IndexOutOfBoundsException
 if the specified index is negative.public int length()
BitSet
: the index of
the highest set bit in the BitSet
plus one. Returns zero
if the BitSet
contains no set bits.
BitSet
.public boolean isEmpty()
BitSet
contains no bits that are set
to true
.
BitSet
is empty.public boolean intersects(BitSet set)
BitSet
has any bits set to
true
that are also set to true
in this
BitSet
.
set
 BitSet
to intersect with
BitSet
intersects
the specified BitSet
.public int cardinality()
BitSet
.
BitSet
.public void and(BitSet set)
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 or(BitSet set)
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 xor(BitSet set)
true
if and only if one of the following
statements holds:
true
, and the
corresponding bit in the argument has the value false
.
false
, and the
corresponding bit in the argument has the value true
.
set
 a bit set.public void andNot(BitSet set)
BitSet
whose corresponding
bit is set in the specified BitSet
.
set
 the BitSet
with which to mask this
BitSet
.public int hashCode()
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 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
.
hashCode
in class Object
Object.equals(java.lang.Object)
,
Hashtable
public int size()
BitSet
to represent bit values.
The maximum element in the set is the size  1st element.
public boolean equals(Object obj)
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
.
equals
in class Object
obj
 the object to compare with.
true
if the objects are the same;
false
otherwise.size()
public Object clone()
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
.
clone
in class Object
size()
public String toString()
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}
".
toString
in class Object

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