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Java Integer bitCount() Method - GeeksforGeeks

Last Updated : 21 Jan, 2025

The bitCount() method of Integer class of java.lang package returns the count of set bits in a positive number. For negative numbers, it returns the count of set bits in its 2s complement form. This function is sometimes referred to as the population count. 

Syntax:

public static int bitCount(int n)

• Parameter: n: the value whose bits are to be counted
• Return: This method returns the count of set bits in a positive number. For negative numbers, it returns the count of set bits in its 2's complement form.

Example 1: To show the working of java.lang.Integer.bitCount() method. 

// Java program to demonstrate working
// of java.lang.Integer.bitCount() method

import java.lang.Integer;

class Gfg {
    // driver code
    public static void main(String args[])
    {
        int a = 10;

        // Convert integer number to binary  format
        System.out.println(Integer.toBinaryString(a));

        // to print number of 1's in the number a
        System.out.println(Integer.bitCount(a));
    }
}

• Time Complexity: O(1), because the number of bits is fixed (32 bits for int).
• Auxiliary Space: O(1), as no extra space proportional to the input is used.

Example 2:

import java.io.*;

class GFG {
    public static void main(String[] args)
    {
        int num1 = 10; // binary representation: 1010
        int num2 = -10; // binary representation:
                        // 11111111111111111111111111110110

        int result1 = Integer.bitCount(num1);
        int result2 = Integer.bitCount(num2);

        System.out.println("Number of one-bits in num1: "
                           + result1);
        System.out.println("Number of one-bits in num2: "
                           + result2);
    }
}

Number of one-bits in num1: 2
Number of one-bits in num2: 30

• Time Complexity: O(1), because the number of bits is fixed (32 bits for int).
• Auxiliary Space: O(1), as no extra space proportional to the input is used.

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