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?

Solution 1

One line of code using Java 8:

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

Solution 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.

Solution 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();
}

Solution 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! :)

Solution 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();
    }

View more solutions

Comments

[Stephen Buttolph]

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

[Elliott Frisch]

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

[Stephen Buttolph]

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

[deadpixels]

It does not end with Enter indeed :/

[deadpixels]

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

[Elliott Frisch]

@deadpixels Edited to add break.

[Stephen Buttolph]

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

[Stephen Buttolph]

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?

[Radiodef]

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

[dbank]

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

[Radiodef]

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.)

[dbank]

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.

[skaffman]

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

[Foon]

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)

[Brett Y]

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

[Wumba]

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