deadpixels deadpixels - 5 months ago 23
Java Question

Read all lines with BufferedReader

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?

Answer

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.

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