Definitely new to Java "Main" Java.lang NullPointerException Error

[lilyumestar]

This project is due by Tuesday and I haven't even gotten half of it done. Can anyone please help me with this Exception error? I've been trying to figure it out for several hours

Error Message

"Main" Java.lang NullPointerException
at Project1.sortingByZipCode<Project1.java:80>
at Project1.main<Project1.java:31>

Here is the Source Code


// StringTokenizerDemo2.java

import java.util.StringTokenizer;
import javax.swing.JOptionPane;


public class Project1
{

public static void main(String[] args)
{
final int MAX_NUMBER_OF_NUMBERS = 40;

if ( args.length == 0 )
{
System.out.println("This program sorts short integers");
System.out.println("from the file specified by a");
System.out.println("command-line argument.");
System.exit(0);
} // if

final String inputFileName = args[0];
final String outputFileName = "sorted-" + inputFileName;

String[] numbersArray = new String[MAX_NUMBER_OF_NUMBERS];

// Read numbers into numbersArray from input file:
int subArrayLength = readFile(inputFileName, numbersArray);

//Sorts the zipcode by compareTo method
sortByZipCode(numbersArray, subArrayLength);


} // method main





private static int readFile(String filename, String[] capacities)
{
TextFileInput in = new TextFileInput(filename);

// Read capacities into array:
int lengthFilled = 0;
String line = in.readLine(); // read first line in file
while ( lengthFilled < capacities.length && line != null )
{

line = in.readLine(); // read next line in file
lengthFilled++;
} // while

// Check to see if all the capacities in the file were read.
// If not, then the array wasn't big enough to hold them all.
// In that case, print an error message and quit.
if ( line != null ) // i.e. if end-of-file not reached
{
System.out.println("File contains too much capacity.");
System.out.println("This program can process only "
+ capacities.length + " capacities.");
System.exit(1);
} // if

// Release file for re-use:
in.close();

return lengthFilled;
} // method inputFromFile




private static void sortByZipCode (String[] lines, int length)
{
for ( int i = 0; i < length-1; i++ )
{
for ( int j = i + 1; j < length; j++ )
{
if ( lines[j].compareTo(lines[i]) > 0 )
{
String Temp = lines[i];
lines[i] = lines[j];
lines[j]= Temp;
}

}//for loop with the j

}//for loop with the i
}//Method SortByZipCode
}//Project1

Thank you very much.

[Eranga]

What's TextFileInput? Is it another class in your application?

And it's much better explain your question specifically, I mean where are you stuck. It's easy to help for others.

[masijade]

You are reading the info from the file, but never assigning the line read to your array. I.E. you are missing a

capacities[index] = line;

myself I would change

line = in.readLine(); // read next line in file
lengthFilled++;

to

capactities[lengthFilled++] = in.readLine(); // read next line in file

[Norm]

Project1.sortingByZipCode<Project1.java:80>

What object is referenced at line 80? Is it null?
How did you come to be null? Can you test for it being null?

[masijade]

Well, it has the method name in it and the only line in that method that will cause an NPE (unless the array itself is null, which it is not, as far as I can see) is this part

 lines[j].compareTo(lines[i])

which will only cause an NPE when the element is null. I am about 99% certain the error has been found.