Question

I have two Java class files: primegen and primecheck sitting in the same directory. primegen calls a public static function from primecheck. primecheck compiles fine.

However, I receive the following compilation error in primegen:

primegen.java:31: cannot find symbol
symbol  : variable primecheck
location: class primegen
          } while (!primecheck.prime(primeCandidate));
                ^

Shouldn’t Java be checking other (compiled) classes within the same directory? Does Java have a problem with primecheck being in lower-case letters (e.g. Is it treating primecheck as a variable instead of a class?)?

Update with Complete Code

Code for primegen:

import java.math.BigInteger;
import java.util.Random;

public class primegen
{

    public static void main(String args[])
    {
        try
        {
            int numBits = Integer.parseInt(args[0].trim());
            System.out.println(generatePrime(numBits));
        }
        catch (Exception e)
        {
            System.out.println("You must enter a positive integer number of bits.");
        }
    }

    private static BigInteger generatePrime(int numBits) throws Exception
    {
        if (numBits < 1)
            throw new Exception("You must enter a positive integer number of bits.");

        BigInteger primeCandidate;
        Random rand = new Random();

        do
        {
            primeCandidate = new BigInteger(numBits, rand);
        } while (!primecheck.prime(primeCandidate));

        return primeCandidate;
    }

}

Code for primecheck:

import java.math.BigInteger;
import java.util.Random;

public class primecheck
{

    public static void main(String args[])
    {
        try
        {
            BigInteger primeCandidate = new BigInteger(args[0].trim());
            if (prime(primeCandidate))
                System.out.println("True");
            else
                System.out.println("False");
        }
        catch (Exception e)
        {
            System.out.println("You must enter a positive integer.");
        }
    }

    public static boolean prime(BigInteger n) throws Exception
    {
        if (n.compareTo(BigInteger.ZERO) == -1)
            throw new Exception("You must enter a positive integer.");
        else if (n.equals(BigInteger.ZERO) || n.equals(BigInteger.ONE))
            return false;

        int maxIterations = 1000;
        BigInteger a;

        for (int i = 0; i < maxIterations; i++)
        {
            a = randomBase(n);
            a = a.modPow(n.subtract(BigInteger.ONE), n);

            if (!a.equals(BigInteger.ONE))
                return false;
        }

        return true;
    }

    private static BigInteger randomBase(BigInteger n)
    {
        Random rand = new Random(); 
        BigInteger a;

        do
        {
            a = new BigInteger(n.bitLength(), rand);
        } while ( !(BigInteger.ONE.compareTo(a) <= 0 && a.compareTo(n) < 0) );

        return a;
    }

}

Answer 1

Java does not care about names being all lowercase or uppercase. These are just naming conventions (Java is case sensitive, but will not enforce any particular naming convention).

Edit: (after a few iterations 🙂

The code you posted compiles fine. The problem is obviously somewhere else (javac command line arguments, classpath…)