Java Long bitCount() Method

The Long.bitCount() method in Java is used to count the number of one-bits in the two's complement binary representation of a specified long value.

Table of Contents

1. Introduction
2. bitCount() Method Syntax
3. Examples
   • Counting Bits in a Positive Long
   • Counting Bits in a Negative Long
   • Counting Bits in Zero
4. Real-World Use Case
5. Conclusion

Introduction

The Long.bitCount() method is a static method in the Long class in Java. It returns the number of one-bits in the two's complement binary representation of the specified long value. This method is useful for various bit manipulation tasks, such as in cryptography, error detection, and computer graphics.

bitCount()() Method Syntax

The syntax for the Long.bitCount() method is as follows:

public static int bitCount(long i)

• i: The long value whose one-bits are to be counted.

The method returns:

• The number of one-bits in the two's complement binary representation of the specified long value.

Examples

Counting Bits in a Positive Long

The bitCount() method can be used to count the number of one-bits in a positive long value.

Example

public class BitCountExample {
    public static void main(String[] args) {
        long number = 29L; // Binary representation: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00011101
        int bitCount = Long.bitCount(number);

        System.out.println("Number of one-bits in " + number + ": " + bitCount);
    }
}

Output:

Number of one-bits in 29: 4

In this example, the long value 29 has a binary representation of 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00011101, which contains four one-bits.

Counting Bits in a Negative Long

The bitCount() method can also be used to count the number of one-bits in a negative long value.

Example

public class NegativeBitCountExample {
    public static void main(String[] args) {
        long number = -29L; // Binary representation (two's complement): 11111111 11111111 11111111 11111111 11111111 11111111 11111111 11100011
        int bitCount = Long.bitCount(number);

        System.out.println("Number of one-bits in " + number + ": " + bitCount);
    }
}

Output:

Number of one-bits in -29: 61

In this example, the long value -29 has a binary representation of 11111111 11111111 11111111 11111111 11111111 11111111 11111111 11100011 (two's complement), which contains sixty-one one-bits.

Counting Bits in Zero

The bitCount() method can be used to count the number of one-bits in zero.

Example

public class ZeroBitCountExample {
    public static void main(String[] args) {
        long number = 0L; // Binary representation: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
        int bitCount = Long.bitCount(number);

        System.out.println("Number of one-bits in " + number + ": " + bitCount);
    }
}

Output:

Number of one-bits in 0: 0

In this example, the long value 0 has a binary representation of 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000, which contains zero one-bits.

Real-World Use Case

Error Detection in Data Transmission

In a real-world application, you might use the Long.bitCount() method to implement error detection algorithms, such as parity checks, which rely on counting the number of one-bits in a data stream.

Example

public class ParityCheckExample {
    public static void main(String[] args) {
        long data = 0b1101011001101L; // Example data with an odd number of one-bits

        boolean isOddParity = Long.bitCount(data) % 2 != 0;

        if (isOddParity) {
            System.out.println("The data has odd parity.");
        } else {
            System.out.println("The data has even parity.");
        }
    }
}

Output:

The data has odd parity.

In this example, the method counts the number of one-bits in the binary data 0b1101011001101 and determines that it has odd parity.

Conclusion

The Long.bitCount() method in Java is a powerful and useful tool for counting the number of one-bits in the binary representation of a long value. By understanding how to use this method, you can efficiently handle tasks that involve bit manipulation in your Java applications. Whether you are dealing with positive or negative long values, or implementing error detection algorithms, the bitCount() method provides a reliable solution for these tasks.