Cognitive Complexity

Cognitive Complexity is a measure of how hard the control flow of a method is to understand. Methods with high Cognitive Complexity will be difficult to maintain.

A developer can reduce the Cognitive Complexity in following ways.

• Deep nesting: Use early returns or guard clauses
• Repeated logic: Extract into helper functions
• Multiple concerns: Break the method into smaller methods
• Verbose conditions: Use descriptive variable/method names

A Java code example with high cognitive complexity

This is a Java code example, that is nested, hard-to-read method that checks prime numbers, counts them, and handles edge cases.

public int countPrimes(int[] numbers) {
    int count = 0;
    for (int i = 0; i < numbers.length; i++) {
        if (numbers[i] > 1) {
            boolean isPrime = true;
            for (int j = 2; j < numbers[i]; j++) {
                if (numbers[i] % j == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime) {
                count++;
            }
        } else {
            if (numbers[i] == 0) {
                System.out.println("Zero found");
            } else {
                System.out.println("Negative or One found");
            }
        }
    }
    return count;
}

Refactored the above java code (low congitive complexity)

public int countPrimes(int[] numbers) {
    int count = 0;
    for (int num : numbers) {
        if (isPrime(num)) {
            count++;
        } else {
            handleNonPrime(num);
        }
    }
    return count;
}

private boolean isPrime(int num) {
    if (num <= 1) return false;
    for (int i = 2; i < num; i++) {
        if (num % i == 0) return false;
    }
    return true;
}

private void handleNonPrime(int num) {
    if (num == 0) {
        System.out.println("Zero found");
    } else {
        System.out.println("Negative or One found");
    }
}