Java在int中找到第二位数字

Question

I am working on a Java problem in which I need to check if the second-leading digit of an int (ex: the '2' in 123, or the '8' in 58347) of any size is a particular digit (such as a '2' or a '5'), and then assign true to a Boolean, if it is that digit. I am trying to do the modulo/divisor method, but I am not able to extract the second-leading digit if the number is large.

I searched Stack Overflow, and found a very similar question. However, the solution for that question works if the number is hard-coded as being two digits. I know there is a way by converting int to String, and I tried that method successfully, but I need to use int/modulo/division method. I tried doing (n%100)/10; but it got me second-to-last digit (ex: the '7' in 4562374), not second-after-first digit.

// n is a number such as 123, or 25, or 52856.
while (n > 0) { 
int i=((n%10)/10);
if( (i==2)||(i==3) || (i==5)|| (i==7) )
{ secondDigit=true; }
else { secondDigit= false; } }
System.out.println(secondDigit);

Answer 1

Just keep dividing by 10 until the number is < 100 then do modulo 10, example:

class Main {
  public static void main(String[] args) {
    int n = 58347;
    while (n >= 100) {
      n /= 10;
    }
    System.out.println(n % 10); // prints 8
  }
}

Answer 2

Not certain about the efficiency of this method, however its easy to read.

Integer.parseInt(String.valueOf(Math.abs(initial_value)).charAt(1)+"")

However, you have to ensure that the number has more than 1 digit.

Answer 3

Instead of repeatedly dividing the number you have until it's small enough for you to handle, how about finding out how big the number is so you only need to do a single division?

What I mean is that you should consider using logarithms to find out the magnitude of your number. Finding the base 10 logarithm of your number gets you its magnitude. For 100 the log_10 is 2, so you can do the following:

long magnitude = Math.log10(number);
long divisor = Math.pow(10, magnitude - 1);
long smallNumber = number / divisor;
int digit = smallNumber % 10;