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I'm reading an older version of Java book that was doing some HTML processing.
It uses this while loop conditional statement: (line = r.readLine()) != null.

r is a BufferedReader variable constructed from new BufferedReader(new InputStreamReader(System.in))

In Eclipse console, I'm not sure how to input null to break out of this while loop. (Control C doesn't work)

I find that if I use empty string test of !(line = r.readLine()).isEmpty() or !(line = r.readLine()).equals("") will break out of the while loop if I press Enter twice.
But this uses an empty string, not a null.

Although this seems to be more intuitive, but the HTML script can contain empty line as well, so I won't be able to process HTML scripts that have empty lines if it terminate on empty string.

How can we input null from the console?

Is the program intended to read from a file instead? What's the best way to input and set termination for this?

Update:

As seen from a related question, this problem with Eclipse IDE can be solved via "Control + Z". It inputs "null".

Night0
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    If the code was processing HTML, it was likely reading from a file or URL, which both experience `readLine()` as null when the end of the data is reached. I don't believe you can enter null in any console, as the value defaults to the empty string. Instead, use a different break condition, such as `while (!(line = r.readLine()).equals("quit"))`. Typically, however, `java.util.Scanner` is used for console input rather than `BufferedReader`. – FThompson Mar 08 '14 at 03:14
  • Thank you! Ok, that makes a lot of sense. I thought it's possible because the book's code just reads from System.in – Night0 Mar 08 '14 at 03:18
  • What you're wanting to do is to send an EOF to the standard input stream. I think the linked answer has what you need. – chrylis -cautiouslyoptimistic- Mar 08 '14 at 03:26
  • Thanks chrylis!~ Yeah, Control + Z does work! – Night0 Mar 08 '14 at 03:32

1 Answers1

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Do a if and else statement. You could use a void so It would be like this:

public void v1(){
/* code goes here */
if(line) // or whatever{
   //code
 }else{
  System.out.println("[ERROR] Null");
  }
}

I'm not completely sure what you're trying to do. But to print a basic null into the console, then just do System.out.print(); or System.out.println();

Simple as that.

UltimateEspresso
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  • Thanks. Sorry, I wasn't trying to output null. I was trying to input null from console. (Control Z works in Eclipse) – Night0 Mar 08 '14 at 19:40