Java BufferedReader to String Array

Question

I was looking through a lot of diffrent subjects here on stackoverflow but couldn't find anything helpful so far :/

So this is my problem. I am writing a filecopier. The problem occurs already at reading the file. My test docoument got 3 lines of random text. All those 3 lines should get written in a string array. The problem is that only the 2nd line of the textdocument gets written in the array and I can't figure out why. Already debugged it, but didn't get me any further.

I know there are diffrent solutions for a filecopier with diffrent classes etc. But I would really like to get it running with the classes I used here.

    String[] array = new String[5];
    String datei = "test.txt";
    public String[] readfile() throws FileNotFoundException {
    FileReader fr = new FileReader(datei);
    BufferedReader bf = new BufferedReader(fr);
    try {
        int i=0;
        //String  Zeile = bf.readLine();
        while(bf.readLine() != null){
            array[i] = bf.readLine();
        //  System.out.println(array[i]);  This line is for testing
            i++;
        }
        bf.close();

    } catch (IOException e) {
        e.printStackTrace();
    }
    return array;

Matt Ball · Accepted Answer · 2014-08-18 19:13:09Z

12

You're calling readLine() twice for each iteration of the loop, thereby discarding every other line. You need to capture the value returned by every call to readLine(), because each readLine() call advances the reader's position in the file.

Here's the idiomatic solution:

String line;
while((line = bf.readLine()) != null){
    array[i] = line;
    i++;
}

edited Aug 18, 2014 at 19:13

answered Aug 18, 2014 at 19:03

Matt Ball

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2 Comments

Quatsch Over a year ago

Thanks for the super fast and very helpful answer ! Everything works perfectly now. Would upvote and mark as the best answer, if I had any reputation.

Matt Ball Over a year ago

By accepting the answer, you did exactly that :) and if you really feel like you need to upvote as well, you can always come back later when you have sufficient rep.

Jens · Accepted Answer · 2014-08-18 19:05:40Z

1

Here you read 2 lines:

   while(bf.readLine() != null){
        array[i] = bf.readLine();
    //  System.out.println(array[i]);  This line is for testing
        i++;
    }

You have to change your Code to:

   String line = null;
   while((line =bf.readLine()) != null){
        array[i] = line;
    //  System.out.println(array[i]);  This line is for testing
        i++;
    }

answered Aug 18, 2014 at 19:05

Jens

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Comments

hityagi · Accepted Answer · 2014-08-18 19:06:03Z

1

The problem is here :

while(bf.readLine() != null)

readLine() reads a line and returns the same at the same time it moves to the next line.

So instead of just checking if the returned value was null also store it.

String txt = null;
while((txt = bf.readLine()) != null)
    array[i++] = txt;

answered Aug 18, 2014 at 19:06

hityagi

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1 Comment

Quatsch Over a year ago

Instead of giving me the 3 lines of my test file, it gives me 3 lines that say "null". The problem is already solved but I want to learn as much as possible. Would be glad if we could get your solution working, too.

user1219387 · Accepted Answer · 2014-08-18 19:10:30Z

1

I think its because you are calling readLine() twice. First time in the loop, and then second time when you put it in the array. So, it reads a line at the beginning of the loop (line 1), then first line of code inside the loop (line 2 that you see)

answered Aug 18, 2014 at 19:10

user1219387

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Comments

Ronald Coarite · Accepted Answer · 2021-08-23 14:27:18Z

-1

I am use Stream.

Not a. This form only applies to reading text files.

BufferedReader bf = new BufferedReader(fr);
// ...
List<String> lines = bf.lines().collect(Collectors.toList());

edited Aug 23, 2021 at 14:27

answered Aug 9, 2021 at 1:06

Ronald Coarite

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