Read all lines with BufferedReader

Question

I want to type a multiple line text into the console using a BufferedReader and when I hit "Enter" to find the sum of the length of the whole text. The problem is that it seems I'm getting into an infinite loop and when I press "Enter" the program does not come to an end. My code is below:

InputStreamReader instream = new InputStreamReader(System.in);
BufferedReader buffer = new BufferedReader(instream);

    line= buffer.readLine();

    while (line!=null){
        length = length + line.length();
        line= buffer.readLine();
    }

Could you please tell me what I'm doing wrong?

Atc

when you only press enter line will equal "" not null. try changing line != null to !line.equals("") – Titanite

Also, just to provide some other opinions (e.g. using a for loop), codereview.stackexchange.com/questions/44135/… – Herren

I realized last night as I was falling asleep: what are you using length for? NB that if you were to do cat myfile | java yourprogram and print out the value of length, this will disagree with what, e.g. wc prints out, because you're not counting newlines. If you need to do that, note that DOS files will have "\r\n" and UNIX files will have "\n" and my original suggestion to use System.getProperty("line.separator") probably won't work because there's no guarantee that you aren't e.g. trying to read a DOS file under Linux. (So, hopefully that's not what you're mean to do) – Herren

Answer 1

Update Java 16:

line =  buffer.lines().toList();

One line of code using Java 8:

line =  buffer.lines().collect(Collectors.joining());

Samy

Do I need to include a newline as a delimiter to preserve lines? – Tunny

Yes, you have to add a possible separator to preserve lines: buffer.lines() .collect(Collectors.joining(System.lineSeparator())); – Circadian

the first one returns a list and the second one - a string. – Pickering

Answer 2

The idiomatic way to read all of the lines is while ((line = buffer.readLine()) != null). Also, I would suggest a try-with-resources statement. Something like

try (InputStreamReader instream = new InputStreamReader(System.in);
        BufferedReader buffer = new BufferedReader(instream)) {
    long length = 0;
    String line;
    while ((line = buffer.readLine()) != null) {
        length += line.length();
    }
    System.out.println("Read length: " + length);
} catch (Exception e) {
    e.printStackTrace();
}

If you want to end the loop when you receive an empty line, add a test for that in the while loop

while ((line = buffer.readLine()) != null) {
    if (line.isEmpty()) {
        break;
    }
    length += line.length();
}

JLS-14.15. The break Statement says

A break statement transfers control out of an enclosing statement.

Collings

Because the OP is reading from system.in won't this never end? Wouldn't it just wait for the users next input? – Titanite

@StephenB It will end on EOF (or ctrl-d); possibly also with ctrl-c and/or ctrl-brk. – Collings

But I think he wants it to end when he presses Enter. – Titanite

It does not end with Enter indeed :/ – Atc

@Atc Edited to add break. – Collings

Arguably, the idiomatic way is now buffer.lines(). – Delorsedelos

Answer 3

line will not be null when you press enter; it will be an empty string.

Take note of what the BufferedReader JavaDoc says about readLine():

Reads a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

And readLine() returns:

A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached

So when you press [Enter], you are giving the BufferedReader a new line containing only \n, \r, or \r\n. This means that readLine() will return an empty string.

So try something like this instead:

InputStreamReader instream = new InputStreamReader(System.in);
BufferedReader buffer = new BufferedReader(instream);

line = buffer.readLine();

while( (line != null) && (!line.isEmpty()) ){
    length = length + line.length();
    line = buffer.readLine();
}

Disputation

I may be wrong. But I don't think the returned String actually contains the end line character. If it did then a System.out.println(buffer.readLine()); would have another line at the end right? – Titanite

Also in the JavaDoc you linked to: "returns [...] the contents of the line, not including any line-termination characters". – Sheatfish

@StephenB and @RadioDef: Ah my mistake! You are both right. I was confused with read() and who knows what. – Disputation

while(!line.isEmpty()) {...} like you had before you deleted was correct... (Besides the fact that some have also pointed out that readLine can still return null if the user does something obscure.) – Sheatfish

I edited to correct my answer. @StephenB and RadioDef, thank you both for calling me out and correcting me so that I didn't spread misinformation. – Disputation

Answer 4

When you only press Enter the return from buffer.readLine(); isn't null it is an empty String.

Therefore you should change line != null to !line.equals("") (You could also change it to line.length() > 0)

Now your code will look something like this:

InputStreamReader instream = new InputStreamReader(System.in);
BufferedReader buffer = new BufferedReader(instream);

line = buffer.readLine();

while (!line.equals("")){
    length = length + line.length();
    line = buffer.readLine();
}

This should solve your problem. Hope this helped! :)

Titanite

This works indeed, but for some reason I have to press Enter twice. Any idea why that is? – Atc

@Atc When I run the program it terminates at the first empty line. Does the counter go up when you press Enter? – Titanite

Answer 5

Since Java 8 you can use BufferedReader#lines method directly on buffered reader.

    try (InputStreamReader in = new InputStreamReader(System.in);
         BufferedReader buffer = new BufferedReader(in)) {
        final int length = buffer.lines().mapToInt(String::length).sum();
        System.out.println("Read length: " + length);
    } catch (Exception e) {
        e.printStackTrace();
    }

Venicevenin

Answer 6

Snarky answer: what you're doing wrong is only creating 2 objects in Java to do something... if you search, you can probably find a few more classes that extend BufferedReader or ExtendedBufferReader etc., and then it can be real Enterprise Java.

Now that i've gotten that out of my system: more useful answer. System.in is closed when you input EOF, which is Control-D under Linux and I think MacOS, and I think Control-Z plus enter under Windows. If you want to check for enter (or more specifically, two enters... one to finish the last line and one to indicate that you're done, which is essentially how http handles determining when the http headers are finished and it's time for the http body, then @dbank 's solution should be a viable option with a minor fix I'm going to try to make to move the ! inside the while predicate instead of !while.

(Edit #2: realized readLine strips the newline, so an empty line would "" instead of the newline, so now my code devolves to another answer with the EOF bit as an answer instead of comment)

Edit... that's weird, @dbank had answered while I was typing my answer, and I would have stopped had I not though mentioning the EOF alternative. To repeat his code from memory with the edit I was going to make:

InputStreamReader instream = new InputStreamReader(System.in);
BufferedReader buffer = new BufferedReader(instream);

    line= buffer.readLine();
    while (line != null && !line.equals("")){
        length = length + line.length();
        line= buffer.readLine();
    }

Herren

To the down voter(s): if this was because of the snarky answer at the top, byte me (I mean, new Byte []("me".getBytes(Charset.forName("UTF-8"))). Otherwise, I'm curious why the downvotes: My code is similar to others (and when I posted @dbank's answer appeared, disappered, and now reappearered; you can't see it now at the 9 hour mark, but my answer was posted marginally before the others) and I also mention the EOF option (which is also useful when piping) – Herren

Answer 7

Put every lines into String[] array. and second method get the number of lines contains in text file. I hope this might be useful to anyone..

public static void main(String... args) throws IOException {
    String[] data = getLines();
    for(String v : data) {
        out.println(v);
    }
}

public static String[] getLines() throws IOException {
    BufferedReader bufferReader = new BufferedReader(new FileReader("C:\\testing.txt"));
    String line = bufferReader.readLine(); 
    String[] data = new String[getLinesLength()];
    int i = 0;
    while(line != null) {
        data[i] = line; 
        line = bufferReader.readLine();
        i++;
    }
    bufferReader.close();
    return data;
}

public static int getLinesLength() throws IOException {
    BufferedReader bufferReader = new BufferedReader(new FileReader("C:\\testing.txt"));
    String line = bufferReader.readLine(); 
    int size = 0;
    while(line != null) {
        size += 1;
        line = bufferReader.readLine();
    }
    bufferReader.close();
    return size;
}

Mortmain

Answer 8

Good example from @Russel Yang (https://mcmap.net/q/366048/-read-all-lines-with-bufferedreader).

Use this code, to add also a new line character after each line.

String lines = bufferedReader.lines().map(line -> line + "\n").collect(Collectors.joining());

Maurizia