Fixing a Null Pointer Exception in Java

Question

I'm learning about BufferedReaders and a few other classes and am making a small program that takes a text file with information about courses I've taken and calculates my GPA. Here's what I have so far:

import java.util.ArrayList;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

class GradeFormatter {

    public static ArrayList<String[]> courses;
    public static double unitsAttempted;
    public static double unitsPassed;
    public static double gradePoints;
    public static double gpa;

    public static void main(String[] args) {
        try {
            FileReader fileReader = new FileReader("grades.txt");
            BufferedReader reader = new BufferedReader(fileReader);
            while (true) {
                String line = reader.readLine();
                if (line == null) {
                    break;
                } else {
                    processLine(line);
                }
            }
            reader.close();
        } catch (IOException e) {
            System.out.println("File does not exist.");
        }
    }

    public static void processLine(String line) {
        String[] newCourse = line.split("\\t");
        courses.add(newCourse);
    }

}

I'm getting the following output when I try to run the program:

Exception in thread "main" java.lang.NullPointerException
    at GradeFormatter.processLine(GradeFormatter.java:34)
    at GradeFormatter.main(GradeFormatter.java:23)

Could anyone help me out with why I'm getting this null pointer exception? I cannot seem to figure out where it's coming from.

Something is null. The stack-trace tells you where. Use the debugger to determine which thing is null. — Oliver Charlesworth, Jun 01 '14 at 11:52
You have not initialized `courses`. You're trying to add elements to a list that doesn't exist yet. — Ant P, Jun 01 '14 at 11:53

score 1 · Answer 1 · answered Jun 01 '14 at 11:53

1

You should initilize the ArrayList courses ArrayList<String[]> courses = new ArrayList<String[]>()

answered Jun 01 '14 at 11:53

Jens

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Fixing a Null Pointer Exception in Java

1 Answers1