Count the Number of Bits Set to One using Java

In this article, we’ll be counting the number of bits set to one using Java. To make it clearer, let’s take number 6 as an example. Number 6 is written as 110₂ in binary. From our example, we’ll get the output as 2, as there are 2 ones in the binary of the converted number. In this process, we use 2 concepts related to the binary numbers.   

• Binary Comparison
• Binary Shifting

What is Binary Comparison?

In our example, we are using and operation (&) for the binary comparison. It also called as bitwise and operation. Let’s take a look at the below example to understand how this binary comparison works with the & operator.

For Eg: Let’s take n as 4 and evaluate the (n&1) operation.

Logic Gate of AND operation

n = 00000000  00000100

A	B	Result
0	0	0
0	1	0
1	0	0
1	1	1

1 = 00000000  00000001 AND

------------------------------

0 = 00000000  00000000

==================

From the bitwise-and, result of (n&1); where n=4 is 0. This is frequently used to extract the Least Significant Bit (LSB) from a given number.

What is Binary Shifting?

Binary shifting refers to as shifting of all the bits in the operand used to a particular direction assigned by the user. There are 2 types of shifting.

• ·         Arithmetic Left shifting(<<)
• ·         Arithmetic Right shifting(>>)

In our example, arithmetic Right shifting is used to shift all the bits to the right side. To understand how arithmetic right shifting works, take a look at the below example.

When n = 12                                            Binary Representation = 1100

Let’s apply right shifting to the 12 => 1100>>1 which shifts one bit to right at a time.

1^st Iteration – Last 0 is removed (110)

2^nd Iteration – Next 0 is removed (11)

public static void main(String args[]){

      System.out.print("Please enter the number: ");

      //take the input from the user

      Scanner input = new Scanner(System.in);

      int number = input.nextInt();

             

      System.out.print("Total number of 1s

                            : "+countBitsSetToOne(number));

      //close the scanner instance

      input.close();

}

       

public static int countBitsSetToOne(int number) {

      int count = 0;

      while (number > 0){

        //binary comparison

        count = count + (number & 1);

        //binary shifting

        number = number >> 1;

      }

      return count;

}

In here, we have created a static method which takes one integer parameter. First, it checks whether the number is equal to zero or not. If the number is equal to zero, it will return the default value of the count variable; which is zero. When the number is greater than zero, it will increase the count while doing the bitwise-and operation. As I said earlier, bitwise-and returns the LSB of the number passed in. Finally, binary shifting is done to shift all the bits to right one by one until the whole iteration ends. When the number becomes zero, while loop terminates and returns the count.