I Am Not Getting the Result I Expect Using readLine() in Java

Question

I am using the code snippet below, however it\'s not working quite as I understand it should.

public static void main(String[] args) {
    BufferedReader         


        

Answer 1

No input is not the same as the end of the stream. You can usually simulate the end of the stream in a console by pressing Ctrl+D (AFAIK some systems use Ctrl+Z instead). But I guess this is not what you want so better test for empty strings additionally to null strings.

Answer 2

From my understanding of this, readLine should return null the first time no input is entered other than a line termination, like '\r'.

That is not correct. readLine will return null if the end of the stream is reached. That is, for example, if you are reading a file, and the file ends, or if you're reading from a socket and the socket closses.

But if you're simply reading the console input, hitting the return key on your keyboard does not constitute an end of stream. It's simply a character that is returned (\n or \r\n depending on your OS).

So, if you want to break on both the empty string and the end of line, you should do:

while (line != null && !line.equals(""))

Also, your current program should work as expected if you pipe some file directly into it, like so:

java -cp . Echo < test.txt

Answer 3

There's a nice apache commons lang library which has a good api for common :) actions. You could use statically import StringUtils and use its method isNotEmpty(String ) to get:

while(isNotEmpty(line)) {
    System.out.println(line);
    line = br.readLine();
}

It might be useful someday:) There are also other useful classes in this lib.