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Java.util.BitSet class in Java with Examples | Set 1

Last Updated : 23 Jul, 2025

BitSet is a class defined in the java.util package. It creates an array of bits represented by boolean values.

Constructors: 

 BitSet class Constructors
    /                  \ 
 BitSet()          BitSet(int no_Of_Bits)

• BitSet() : A no-argument constructor to create an empty BitSet object. 
   
• BitSet(int no_Of_Bits): A one-constructor with an integer argument to create an instance of the BitSet class with an initial size of the integer argument representing the number of bits. 

// Java program illustrating Bitset Class constructors.
import java.util.*;
public class GFG
{
    public static void main(String[] args)
    {
        // Constructors of BitSet class
        BitSet bs1 = new BitSet();
        BitSet bs2 = new BitSet(6);

        /* set is BitSet class method
           explained in next articles */
        bs1.set(0);
        bs1.set(1);
        bs1.set(2);
        bs1.set(4);

        // assign values to bs2
        bs2.set(4);
        bs2.set(6);
        bs2.set(5);
        bs2.set(1);
        bs2.set(2);
        bs2.set(3);

        // Printing the 2 Bitsets
        System.out.println("bs1  : " + bs1);
        System.out.println("bs2  : " + bs2);
    }
}

Output: 

bs1 : {0, 1, 2, 4}
bs2 : {1, 2, 3, 4, 5, 6}

Important Points :  

• The size of the array is flexible and can grow to accommodate additional bit as needed.
• As it is an array, the index is zero-based and the bit values can be accessed only by non-negative integers as an index.
• The default value of the BitSet is boolean false with a representation as 0 (off).
• Calling the clear method makes the bit values set to false.
• BitSet uses about 1 bit per boolean value.
• To access a specific value in the BitSet, the get method is used with an integer argument as an index.

What happens if the array index in bitset is set as Negative?

The program will throw java.lang.NegativeArraySizeException 

// Java program illustrating Exception when we access
// out of index in BitSet class.
import java.util.*;

public class GFG
{
    public static void main(String[] args)
    {
        // Constructors of BitSet class
        BitSet bs1 = new BitSet();

        // Negative array size
        BitSet bs2 = new BitSet(-1);

        /* set is BitSet class method
           explained in next articles */
        // assigning values to bitset 1
        bs1.set(0);
        bs1.set(1);

        // assign values to bs2
        bs2.set(4);
        bs2.set(6);

        System.out.println("bs1  : " + bs1);
        System.out.println("bs2  : " + bs2);
    }
}

Output: 

Exception in thread "main" java.lang.NegativeArraySizeException: nbits < 0: -1
    at java.util.BitSet.(BitSet.java:159)
    at GFG.main(NewClass.java:9)

BitSet class methods in Java with Examples | Set 2

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