Java - The BitSet Class


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A BitSet class creates a special type of array that holds bit values. The BitSet array can increase in size as needed. This makes it similar to a vector of bits. This is a legacy class but it has been completely re-engineered in Java 2, version 1.4.

The BitSet defines two constructors a shown below.

SR.NO Constructor and Description
1 BitSet( )

This constructor creates a default object

2 BitSet(int size)

This constructor allows you to specify its initial size, i.e., the number of bits that it can hold. All bits are initialized to zero

BitSet implements the Cloneable interface and defines the methods listed in table below:

SN Methods with Description
1 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.

2 void andNot(BitSet bitSet)

For each 1 bit in bitSet, the corresponding bit in the invoking BitSet is cleared.

3 int cardinality( )

Returns the number of set bits in the invoking object.

4 void clear( )

Zeros all bits.

5 void clear(int index)

Zeros the bit specified by index.

6 void clear(int startIndex, int endIndex)

Zeros the bits from startIndex to endIndex.1.

7 Object clone( )

Duplicates the invoking BitSet object.

8 boolean equals(Object bitSet)

Returns true if the invoking bit set is equivalent to the one passed in bitSet. Otherwise, the method returns false.

9 void flip(int index)

Reverses the bit specified by index. (

10 void flip(int startIndex, int endIndex)

Reverses the bits from startIndex to endIndex.1.

11 boolean get(int index)

Returns the current state of the bit at the specified index.

12 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.
13 int hashCode( )

Returns the hash code for the invoking object.

14 boolean intersects(BitSet bitSet)

Returns true if at least one pair of corresponding bits within the invoking object and bitSet are 1.

15 boolean isEmpty( )

Returns true if all bits in the invoking object are zero.

16 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 1 bit.

17 int nextClearBit(int startIndex)

Returns the index of the next cleared bit, (that is, the next zero bit), starting from the index specified by startIndex

18 int nextSetBit(int startIndex)

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

19 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.

20 void set(int index)

Sets the bit specified by index.

21 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.

22 void set(int startIndex, int endIndex)

Sets the bits from startIndex to endIndex.1.

23 void set(int startIndex, int endIndex, boolean v)

Sets the bits from startIndex to endIndex.1, to the value passed in v. true sets the bits, false clears the bits.

24 int size( )

Returns the number of bits in the invoking BitSet object.

25 String toString( )

Returns the string equivalent of the invoking BitSet object.

26 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

Example:

The following program illustrates several of the methods supported by this data structure:

import java.util.BitSet;

public 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);
  }
}

This would produce the following result:

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:
{}

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