NullPointerException when storing lines in an arraylist [duplicate]

Question

I'm getting a NullPointerException in java (at this line :FileReader fstream = new FileReader(fileName)) when I try to read a text file line by line and store them in an arraylist with this code :

public ArrayList<String> StoreLineByLine(String fileName) throws IOException {
    String str;

    ArrayList<String> Line = new ArrayList<String>();
    FileReader fstream = new FileReader(fileName);
    BufferedReader myFileReader = new BufferedReader(fstream);

    while ((str = myFileReader.readLine()) != null) {
        Line.add(str);
    }
    myFileReader.close();
    return Line;
}

Could anyone help me understand the problem ? Thanks a lot !

Please add an error log and tell us which line exactly throws the nullPointerException. — rhbvkleef
– rhbvkleef, Commented Jun 23, 2014 at 14:17
Try researching like I did, stackoverflow.com/questions/218384/… — Rick S
– Rick S, Commented Jun 23, 2014 at 14:18
Works perfectly for me, tried it on my system, calling StoreLineByLine(String fileName) from main() . Check your fileName. — Mustafa sabir
– Mustafa sabir, Commented Jun 23, 2014 at 14:25
Tested on OS X. If fileName is NULL, it yields a NPE on that line. See my answer. — Alvin Thompson
– Alvin Thompson, Commented Jun 23, 2014 at 14:57

Alvin Thompson · Accepted Answer · 2014-06-23 15:35:29Z

2

If you're getting a NPE on that line, then fileName must be null.

BTW, if you're using JDK 8 then this may be a better way to load the lines. Replace the contents of your method with this:

return Files.readAllLines(Paths.get(fileName), Charset.defaultCharset());

...and change the method's return type from ArrayList<String> to List<String>.

edited Jun 23, 2014 at 15:35

answered Jun 23, 2014 at 14:25

Alvin Thompson

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7 Comments

user3767791 Over a year ago

Hello, it's the first time I use this website so I don't know how to log the error. The error is on that line : fstream = new FileReader(fileName); I don't understand how come it is null!

user3767791 Over a year ago

Well it still doesn't work :/

Jayaram Over a year ago

whats new issue you are getting?

user3767791 Over a year ago

I still get the NPE error on that line

Jayaram Over a year ago

@user3767791 never pass fileName as null ... have a null check first in the method

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