Fastest way to get number of digits on a number? [duplicate]

问题

This question already has answers here:

Way to get number of digits in an int? (28 answers)

Closed 6 years ago.

I have do detect the amount of digits on a number. For example, 329586 has 6 digits.

What I done, is simply parsing the number to string, and getting the string length, like:

number.toString().length()

But, is there a fastest way to count digits on a number? I have to use this method several times, so I think using toString() can impact performance.

Thanks.

回答1:

Math.floor(Math.log10(number) + 1)
// or just (int) Math.log10(number) + 1

For example:

int number = 123456;
int length = (int) Math.log10(number) + 1;
System.out.println(length);

OUTPUT:

6

回答2:

how about this homebrewed solution:

int noOfDigit = 1;
while((n=n/10) != 0) ++noOfDigit;

回答3:

Try this :

Working Example

public class Main {
    public static void main(String[] args) {
        long num = -23;
        int digits = 0;
        if (num < 0) 
            num *= (-1);
        if (num < 10 && num >= 0)
            digits = 1;
        else {
            while(num > 0) {
                num /= 10;
                digits++;
            }
        }
        System.out.println("Digits: " +digits);
    }
}

来源：https://stackoverflow.com/questions/15587818/fastest-way-to-get-number-of-digits-on-a-number