CODEWITHSUNDEEP
javanullpointerexceptiontext-files
stealingbikes
stealingbikes

Reputation: 103

Parsing a text file in Java - need help understanding NullPointerException

I'm fairly new to Java and I'm having a difficult time understanding the scanner and exceptions. It's showing a NullPointerException at "while (! line.matches("[\n\r]+"))". I'm not really sure why this is happening. I've initialized the line variable and I'm assuming that if the next line of the scanner is a break line, the while loop should end. If the next line is null then the entire outer loop should end. Why is this returning a NullPointerException? 

public class Readfile {
private static int inputs = 0;

public void main(String filename) throws Exception {
    URL url = getClass().getResource(filename);
    File file = new File(url.getPath());
    parsefile(file);

}

void parsefile(File file) throws Exception {
    ArrayList<String[]> Inputs = new ArrayList<String[]>();
    BufferedReader br = new BufferedReader(new FileReader(file));
    String line = br.readLine();
    while (line != null){
        LinkedList currentinput = new LinkedList();
        if (line.contains("Input")){
            while (! line.matches("[\\n\\r]+")) {
                System.out.println(line);
                line = br.readLine();
            }
        }else{
            line = br.readLine();
        }
    }
}

}

Upvotes: 1

Views: 54

Answers (1)

Elliott Frisch
Elliott Frisch

Reputation: 201447

Your inner loop also calls br.readLine(), so you need to check for null. Change

while (! line.matches("[\\n\\r]+")) {

to something like

while (line != null && ! line.matches("[\\n\\r]+")) {

or

while (! line.matches("[\\n\\r]+")) {
    System.out.println(line);
    line = br.readLine();
    if (line == null) {
        break;
    }
}

Upvotes: 4

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