BitSet - java.util

BitSet

A BitSet class creates a special type of array that holds bit values in the form of boolean values. This array can increase in size as needed. This makes it similar to a vector of bits. The BitSet constructors are shown here:

BitSet( ) BitSet(int size)

The first version creates a default object. The second version allows you to specify its initial size (that is, the number of bits that it can hold). All bits are initialized to false.

BitSet defines the methods listed in Table 19-2.

Method : Description

void and(BitSet bitSet) : ANDs the contents of the invoking BitSet object with those specified by bitSet. The result is placed into the invoking object.

void andNot(BitSet bitSet) : For each set bit in bitSet, the corresponding bit in the invoking BitSet is cleared.

int cardinality( ) : Returns the number of set bits in the invoking object.

void clear( ) : Zeros all bits.

void clear(int index) : Zeros the bit specified by index.

void clear(int startIndex, int endIndex) : Zeros the bits from startIndex to endIndex –1.

Object clone( ) : Duplicates the invoking BitSet object.

boolean equals(Object bitSet) : Returns true if the invoking bit set is equivalent to the one passed in bitSet. Otherwise, the method returns false.

void flip(int index) : Reverses the bit specified by index.

void flip(int startIndex, int endIndex) : Reverses the bits from startIndex to endIndex –1.

boolean get(int index) : Returns the current state of the bit at the specified index.

BitSet get(int startIndex, int endIndex) : Returns a BitSet that consists of the bits from startIndex to endIndex –1. The invoking object is not changed.

int hashCode( ) : Returns the hash code for the invoking object.

boolean intersects(BitSet bitSet) : Returns true if at least one pair of corresponding bits within the invoking object and bitSet are set.

boolean isEmpty( ) : Returns true if all bits in the invoking object are cleared.

int length( ) : Returns the number of bits required to hold the contents of the invoking BitSet. This value is determined by the location of the last set bit.

int nextClearBit(int startIndex) : Returns the index of the next cleared bit (that is, the next false bit), starting from the index specified by startIndex.

int nextSetBit(int startIndex) : Returns the index of the next set bit (that is, the next true bit), starting from the index specified by startIndex. If no bit is set, –1 is returned.

void or(BitSet bitSet) : ORs the contents of the invoking BitSet object with that specified by bitSet. The result is placed into the invoking object.

int previousClearBit(int startIndex) : Returns the index of the next cleared bit (that is, the next false bit) at or prior to the index specified by startIndex. If no cleared bit is found, –1 is returned.

int previousSetBit(int startIndex) : Returns the index of the next set bit (that is, the next true bit) at or prior to the index specified by startIndex. If no set bit is found, –1 is returned.

void set(int index) : Sets the bit specified by index.

void set(int index, boolean v) : Sets the bit specified by index to the value passed in v. true sets the bit; false clears the bit.

void set(int startIndex, int endIndex) : Sets the bits from startIndex to endIndex –1.

void set(int startIndex, int endIndex, : Sets the bits from startIndex to endIndex –1 to the value

boolean v) : passed in v. true sets the bits; false clears the bits.

int size( ) :  : Returns the number of bits in the invoking BitSet object.

IntStream stream( ) : Returns a stream that contains the bit positions, from low to high, that have set bits. (Added by JDK 8.)

byte[ ] toByteArray( ) : Returns a byte array that contains the invoking BitSet object.

long[ ] toLongArray( ) : Returns a long array that contains the invoking BitSet object.

String toString( ) : Returns the string equivalent of the invoking BitSet object.

static BitSet valueOf(byte[ ] v) : Returns a BitSet that contains the bits in v.

static BitSet valueOf(ByteBuffer v) : Returns a BitSet that contains the bits in v.

static BitSet valueOf(long[ ] v) : Returns a BitSet that contains the bits in v.

static BitSet valueOf(LongBuffer v) : Returns a BitSet that contains the bits in v.

void xor(BitSet bitSet) : XORs the contents of the invoking BitSet object with that specified by bitSet. The result is placed into the invoking object.

 :

Table 19-2   The Methods Defined by BitSet :

Here is an example that demonstrates BitSet:

// BitSet Demonstration.

import java.util.BitSet;

class BitSetDemo {

public static void main(String args[]) { BitSet bits1 = new BitSet(16);

BitSet bits2 = new BitSet(16);

// set some bits

for(int i=0; i<16; i++) {

if((i%2) == 0) bits1.set(i);

if((i%5) != 0) bits2.set(i);

}

System.out.println("Initial pattern in bits1: ");

 System.out.println(bits1);

System.out.println("\nInitial pattern in bits2: "); System.out.println(bits2);

    AND bits bits2.and(bits1);

System.out.println("\nbits2 AND bits1: ");

System.out.println(bits2);

    OR bits

bits2.or(bits1); System.out.println("\nbits2 OR bits1: "); System.out.println(bits2);

// XOR bits bits2.xor(bits1);

System.out.println("\nbits2 XOR bits1: ");

System.out.println(bits2);

}

}

The output from this program is shown here. When toString( ) converts a BitSet object to its string equivalent, each set bit is represented by its bit position. Cleared bits are not shown.

Initial pattern in bits1: {0, 2, 4, 6, 8, 10, 12, 14}

Initial pattern in bits2:

{1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 14}

bits2 AND bits1:

{2, 4, 6, 8, 12, 14}

bits2 OR bits1:

{0, 2, 4, 6, 8, 10, 12, 14}

bits2 XOR bits1: {}