How to Find Number of Digits in an Integer at Java

By Loop

    public static int countDigitsInt(int input) {
        int count = 0;

        while (input != 0) {
            input /= 10;
            ++count;
        }

        return count;
    }

By Math

System.out.println(((int) (Math.log10(input)) + 1));

By String method

System.out.println(Integer.toString(input).length());

speed

Loop > Math > String method

Explanation

Loop

divide the input by 10 until cannot. Then cound how many times divided

Math

Basic log definition is

$$A=B^x \iff x=\log_B A$$

Therefore, if you log 10 for integer 336 means

$$336=10^x \iff x=\log_{10} 336$$

Thus, log 10 for number will return Number of Digits - 1

String method

String have counting method which is "length()" convert integer to String and use the method.