Java - Null Pointer Exception on String array

Question

This is the code I working on. It's inside a method and the idea is for it to open a file and check the contents, or the lack of, and report back.

However I'm getting a NullPointerException on the line that I pointed to below.

I have no idea how to fix this. I tried debugging which shows that at the time the line is run the 1st element of the String[] contains text, so that's not a problem.

int i = 0;
int numChar=1, numLines;
String[] line = new String[1000];

try {
    BufferedReader in = new BufferedReader(new FileReader(file));
    try {
        while(numChar > 0) {
            //String[] line = new String[1000];
            line[i] = in.readLine();
PROBLEM-->  numChar = line[1].length();
            i++;
        }            
    } catch (EOFException ex) {
        JOptionPane.showMessageDialog( null, "Error" );
        //break;
    }      
}
catch(IOException e) {
    JOptionPane.showMessageDialog( null, "Missing file or no data to read." );
    System.out.println("IO Error - Missing file");
}

Andy Brown · Accepted Answer · 2015-01-31 14:39:33Z

2

I suspect you just need to change the array access index to use i instead of 1.

numChar = line[i].length();

And you should also check for null as the BufferedReader will return (from the docs):

null if the end of the stream has been reached

numChar = line[i] == null ? 0 : line[i].length;

You might want to expand that so you break out of your loop instead of assigning a length of null.

String s = in.readLine();
if (s == null) {
  break;
}
else {
  line[i] = s;
  numChar = line[i++].length();
}

EDIT in response to comments.

At risk of confusing the issue, my preference would be to rewrite your loop. You don't seem to need numChars outside the loop, so I would remove it so as to reduce your method scope's variables. I also suspect you don't want to stop reading on empty lines, just at the end of the stream:

while (true) { // for(;;) if you prefer
    String s = in.readLine();
    //if (s == null || s.length() == 0) break; // stop on empty lines and end of stream
    if (s == null) break; // stop at end of stream only
    line[i++] = s;
}

edited Jan 31, 2015 at 14:39

answered Jan 31, 2015 at 14:18

Andy Brown

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4 Comments

user2627736 Over a year ago

That's my bad, it used to be an 'i' but I changed it to '1' while trying to debug, it gives same error when it's i

Andy Brown Over a year ago

@user2627736. Yes, you'll need to do a null check as well - see my edit with the documentation reference.

RandomHuman Over a year ago

Imho it will be more efficient to rewrite the loop condition instead of if else logic.

Andy Brown Over a year ago

@RandomHuman. I don't disagree, but didn't want to rewrite the OP' s entire program and leave them trying to work out what had been done.

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