import java.io.*;
import java.math.*;
import java.util.*;
// reading file with BigInts via StreamTokenizer + String handling
public class ChkBigPrimes {
    StreamTokenizer in;

    final String FILE_NAME="c:\\bigints.txt";
    final int MAX_LIMIT = 100000;
    public static void main(String[] args) throws IOException {
        new ChkBigPrimes().run();
    }
    void run() throws IOException {
        in = new StreamTokenizer(new BufferedReader(new FileReader(FILE_NAME))); 

        // commands to handle result of in.sval always as String 
        // during read of large integer numbers:
        in.resetSyntax();
        in.wordChars('0', '9');
        in.whitespaceChars('\r', '\r');
        in.whitespaceChars('\n', '\n');
        
        TreeSet<BigInteger> hsPrimes = new TreeSet<BigInteger>();
        BigInteger p;
        int i=0;
        while (in.nextToken() != StreamTokenizer.TT_EOF && i<MAX_LIMIT) {
            //p=new BigInteger(in.sval);
            p=new BigDecimal( (in.sval).toCharArray() ).toBigInteger();
            if (p.isProbablePrime(4)) {
                hsPrimes.add(p);
            }
            i++;
        }
        System.out.println("\nTotal primes in list: "+hsPrimes.size());
    }
} // end of class ChkBigPrimes

import java.io.*;
import java.math.*;
import java.util.*;
// reading file with BigInts via BufferedReader + two char[] arrays
public class ChkBigPrimes2 {
    StreamTokenizer in;
    BufferedReader br;
    final String FILE_NAME="c:\\bigints.txt";
    final int CRLF_LENGTH=2;
    final int MAX_LIMIT = 100000;
    public static void main(String[] args) throws IOException {
        new ChkBigPrimes2().run();
    }
    void run() throws IOException {
        TreeSet<BigInteger> hsPrimes = new TreeSet<BigInteger>();
        br = new BufferedReader(new FileReader(FILE_NAME));
        char[] buf = new char[60];
        BigInteger p;
        int i=0;
        while (br.ready() && i<MAX_LIMIT) {
            br.mark(60);
            br.read(buf, 0, 60);
            int crlf_idx=0;
            for (int j = 0; j < buf.length; j++) {
                if (buf[j]=='\r') {
                    crlf_idx = j;
                }
            }

            char[] buf2 = new char[crlf_idx]; // пришлось создать второй char[],
            System.arraycopy(buf, 0, buf2, 0, crlf_idx); // т.к. не знаю, как по-другому вырезать из 1-го char[] часть его.

            br.reset();
            br.read(buf, 0, crlf_idx + CRLF_LENGTH);
            p=new BigDecimal(buf2).toBigInteger();
            if (p.isProbablePrime(4)) {
                hsPrimes.add(p);
            }
            i++;
        }
        br.close();
        System.out.println("\nTotal primes in list: "+hsPrimes.size());
    }
} // end of class ChkBigPrimes2