[FIXED] How can I get an accurate length of a BigInteger?

Issue

I am trying to create a program which will generate numbers in the Fibonacci sequence until it finds a 1,000 digit number which is in the sequence. The code I have used runs fine and give a valid output, however, I have had trouble retrieving the length of each number; using BigInteger I have converted the BigInteger to a String and used the String.length() method to get the length, however, I have found that this is not giving the real length, and I can not see why.

import java.util.ArrayList;
import java.math.BigInteger;
public class problemTwentyFive {
  public static void main(String [] args) {
     ArrayList<BigInteger> fibonacciNumbers = new ArrayList<BigInteger>();
     boolean validNo = true;
     int x = 2;
     BigInteger tempAns = new BigInteger(""+0);
     fibonacciNumbers.add(new BigInteger(""+x));
     fibonacciNumbers.add(new BigInteger(""+x));
     do {
      tempAns = fibonacciNumbers.get(x-1).add(fibonacciNumbers.get(x-2));
      if (tempAns.toString().length() <= 1000) {
         System.out.println(tempAns.toString().length());
         if(tempAns.toString().length() == 1000) {
            fibonacciNumbers.add(tempAns);
            validNo = false;
            break;
        } else {
           fibonacciNumbers.add(tempAns);
        }
      }
      x++;
      if (tempAns.toString().length() > 1000) {
         validNo = false;
         break;
      }
      System.out.println(tempAns);
   } while (validNo == true);
   System.out.println("The first term in the Fibonacci sequence to contain 1,000 digits is term: " + fibonacciNumbers.size());
  }
}

Is there a better way to get the length of a BigInteger? I have alread reffered to the question thBigInteger: count the number of decimal digits in a scalable method

Update Text text which is outputted after running the program is:

The first term in the Fibonacci sequence to contain 1,000 digits is term: 4781

We know this is false because if we look at the project I am attempting, when we input 4781 as the answer, it is incorrect. Click here to view the project (Project Euler - Problem 25)

Solution

When this code is executed (i.e. the solution is found):

            if ((tempAns.toString().length()) == 1000)
            {
                fibonacciNumbers.add(tempAns);
                validNo = false;
                break;
            }

The tempAns is not printed. That's why your last printed number is only 999 digits long.

If you add a System.out.println("and is: " + tempAns); at the end, just before the end of the main method you will get the desired number. And the answer is thus 4781 + 1 = 4782

Answered By - Burkhard
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)