BitSet nextSetBit() method in Java

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

nextSetBit() method :
This method in BitSet Class is used to return the index of the first bit that is set to true, that occurs on or after the specified starting index. If no such bit exists then -1 is returned.

Syntax:

public int nextSetBit(int fromIndex)

Parameters: This method takes a mandatory parameter fromIndex which is the index to start checking from (inclusive) for the next true bit.

Return Value: This method returns the index of the next set bit, or -1 if there is no such bit

Exception: This method throws IndexOutOfBoundsException if the specified index is negative.

Note : 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
 }

Example 1: To show the implementation of nextSetBit() function :

// Java program illustrating Bitset 
// nextSetBit() function. 
  
import java.util.*; 
public class GFG { 
    public static void main(String[] args) 
    { 
        // Constructors of BitSet class 
        BitSet bs1 = new BitSet(); 
        BitSet bs2 = new BitSet(); 
        BitSet bs3 = new BitSet(); 
  
        /* assigning values to set1*/
        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); 
        bs2.set(12); 
  
        // Printing the 2 Bitsets 
        System.out.println("bs1 : " + bs1); 
        System.out.println("bs2 : " + bs2); 
        System.out.println("bs3 : " + bs3); 
  
        // Performing nextSetBit() on bitsets 
        System.out.println(bs1.nextSetBit(2)); 
        System.out.println(bs2.nextSetBit(0)); 
        System.out.println(bs3.nextSetBit(3)); 
    } 
} 

Output:

bs1 : {0, 1, 2, 4}
bs2 : {1, 2, 3, 4, 5, 6, 12}
bs3 : {}
2
1
-1

Example 2: To show IndexOutOfBoundException:

// Java program illustrating Bitset 
// nextSetBit() function. 
  
import java.util.*; 
public class GFG { 
    public static void main(String[] args) 
    { 
        // Constructors of BitSet class 
        BitSet bs1 = new BitSet(); 
        BitSet bs2 = new BitSet(); 
  
        /* assigning values to set1*/
        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); 
        bs2.set(12); 
  
        // Printing the 2 Bitsets 
        System.out.println("bs1 : " + bs1); 
        System.out.println("bs2 : " + bs2); 
  
        try { 
            // Passing -1 as parameter 
            System.out.println(bs1.nextSetBit(-1)); 
        } 
        catch (Exception e) { 
            System.out.println("Exception when "
                               + "negative index is passed "
                               + "as parameter : " + e); 
        } 
    } 
} 

Output:

bs1 : {0, 1, 2, 4}
bs2 : {1, 2, 3, 4, 5, 6, 12}
Exception when negative index is passed as parameter : java.lang.IndexOutOfBoundsException: fromIndex < 0: -1

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