Question:

Consider the following recursive method in Java:

public static int countDigits(int number) {
    if (number == 0) {
        return 0;
    }
    return 1 + countDigits(number / 10);
}

1. Explain the purpose of the countDigits method.
2. Write a code snippet that uses the countDigits method to count the number of digits in the integer number 123456789.
3. Determine the output of the code snippet from part 2.

Answer:

1. The purpose of the countDigits method is to recursively count the number of digits in an integer.

2. Code snippet to count the number of digits in 123456789:

int count = countDigits(123456789);
System.out.println(count);

3. The output of the code snippet will be:

9

Step-by-step Explanation:

1. The countDigits method takes an integer number as input.
2. The base case of the recursion is when number == 0. In this case, it means that we have counted all the digits and we return 0.
3. If the base case is not met, we divide the number by 10 to remove the rightmost digit and make a recursive call to countDigits with the updated number value.
4. In each recursive call, we increment the returned value by 1 because we have encountered one more digit.
5. This process continues until number becomes 0, at which point all the digits have been counted and the recursive calls start returning their results.
6. Finally, the initial recursive call returns the total count of digits in the original number.
7. In the given code snippet, we use the countDigits method to count the number of digits in 123456789.
8. The method is called with number = 123456789.
9. The recursive calls are made as follows: 123456789 -> 12345678 -> 1234567 -> 123456 -> 12345 -> 1234 -> 123 -> 12 -> 1 -> 0.
10. As number becomes 0, the base case is met and each recursive call starts returning 0.
11. The final return value is then incremented by 1 in each recursive call, resulting in a total count of 9 digits.
12. The output of the code snippet will be 9.