Setting System.in to read from JTextField

Question

I'm looking for direction on how to replace System.in with an InputStream that reads directly from a JTextField.

So far my approach has pretty much been trial and error. I currently have;

JTextField input = new JTextField();

System.setIn(new InputStream() {
  int ptr = 0;
  @Override
  public int read() throws IOException {
     int c;
     try {
        c = input.getText().charAt(ptr);
     }
     catch (IndexOutOfBoundsException ioob) {
        return 0;
     }
     ptr++;
     return c;
  }
});

This yields an NoSuchElementException as in attempts to read when the input is empty and I assume can never find a delimiter.

What approach am I missing?

@evanwong Can you suggest how that can be bound to an inputstream? — Jivings, Jun 08 '12 at 14:54

Jivings · Accepted Answer · 2012-06-08T21:26:12.923

3

Well, this is the method that I used to get it working correctly. If anyone can improve this answer then feel free.

final LinkedBlockingQueue<Character> sb = new LinkedBlockingQueue<Character>();

final JTextField t = new JTextField();
t.addKeyListener(new KeyListener() {
  @Override
  public void keyTyped(KeyEvent e) {
    sb.offer(e.getKeyChar());
  }
  ...
});

System.setIn(new BufferedInputStream(new InputStream() {
  @Override
  public int read() throws IOException {
    int c = -1;
    try {
      c = sb.take();            
    } catch(InterruptedException ie) {
    } 
    return c;           
  }
}));

edited Jun 08 '12 at 21:26

answered Jun 08 '12 at 20:47

Jivings

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You have made different semantic decisions than the specs indicate. And your not following the blocking contract. And return 0 // nothing to return right now, is just a bad decision in my eyes. – Captain Giraffe Jun 08 '12 at 21:20
@CaptainGiraffe I have improved upon my answer. – Jivings Jun 08 '12 at 21:26
@CaptainGiraffe I was incorrect in my 0 assumption. Apologies. – Jivings Jun 08 '12 at 21:27
Apologies are not necessary, but you still have the Cut/Paste scenario to consider. Also you could have made you LBQ yourself =) Isn't there an onChangeListener to simplify things for you? – Captain Giraffe Jun 08 '12 at 21:30
@CaptainGiraffe An on change listener would probably be better! I'll test and edit. Also I did do some stuff with locking first, then I remembered the LBQ =) – Jivings Jun 08 '12 at 21:34

score 1 · Answer 2 · answered Jun 08 '12 at 14:57

1

You look halfway there, but:

From the Javadocs

This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

http://docs.oracle.com/javase/1.4.2/docs/api/java/io/InputStream.html#read%28%29

So your method should just wait for a key to be pressed. Either by handling NoSuchElementException, or a KeyListener that checks how many (new?) characters are available.

The semantics of this InputStream is different from a console one, so you need to make some design decisions on how to handle edits, not just keypresses.

answered Jun 08 '12 at 14:57

Captain Giraffe

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So I should just be catching that exception? – Jivings Jun 08 '12 at 14:58
@Jivings Yes, and not return from the method. Return when you have data. – Captain Giraffe Jun 08 '12 at 15:02
It looks to me as if I should be returning 0 when there is an exception, as the method should return how many bytes have been read. – Jivings Jun 08 '12 at 15:06
@Jivings Your exception is not no data, and no data is not an exception. Don't return. – Captain Giraffe Jun 08 '12 at 21:23

Setting System.in to read from JTextField

2 Answers2

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