Receiving null pointer exception

Question

Created the following program to read and output a file:
import java.io.*;
import java.util.StringTokenizer;
public class ReadSource {
public static void main(String[] arguments) {
     StringTokenizer st1;
     try {
          FileReader file = new
                    FileReader("C:/upload/DS121002.csv");
                    BufferedReader buff = new BufferedReader(file);
                    boolean eof = false;
                    while (!eof) {
                    String line = buff.readLine();
                         if (line == null)
                         eof = true;
                         else
                         System.out.println(line);
                              st1 = new StringTokenizer(line,",");
                              System.out.println("Token 1: " + st1.nextToken());
                              System.out.println("Token 2: " + st1.nextToken());
                    buff.close();
          } catch (IOException e) {
          System.out.println("Error -- " + e.toString());
I am receiving the following error message when the program completes:
Exception in thread "main" java.lang.NullPointerException
at java.util.StringTokenizer.<init>(StringTokenizer.java:122)
at java.util.StringTokenizer.<init>(StringTokenizer.java:138)
at ReadSource.main(ReadSource.java:18)
What do I need to change to prevent this error?

Answer 1

You coded:
if (line == null)
eof = true;
else
do something else;
// then, regardless of the above,
st1 = new StringTokenizer(line,","); // line is still null here
So there's the problem.