TextField setText(null) not working

Question

Very simply put, I want a text field that when you type in it, it stores the character in a global String variable but doesn't actually display it. I know there are several ways of doing this, including a PasswordField, but this is purely for understanding purposes only.
String str = "";
private void txtLineKeyPressed(java.awt.event.KeyEvent evt) {
    char key = evt.getKeyChar();
    str = str + key;
    txtLine.setText(null);
}When typing "asdf" produces (caret is represented by |):
a|
s|
d|
f|I want to understand why txtLine.setText(null) clears the field BEFORE the letter is added to the field and possibly find out if there's a way (using TextField only) to accomplish this. I had a problem earlier with the enter key producing a line break at the end of all my lines and realized I was using a TextArea that caused the problem. Am I doing something similarly wrong?
--dorky                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

Answer 1

I want to understand why txtLine.setText(null) clears the field BEFORE the letter is added to the field Read up on how KeyListeners work. Three events are fired. The Document is updated on keyTyped(), which is generated after the keyPressed() event.
If you need further help then you need to create a [Short, Self Contained, Compilable and Executable, Example Program (SSCCE)|http://homepage1.nifty.com/algafield/sscce.html], that demonstrates the incorrect behaviour.
Don't forget to use the Code Formatting Tags so the posted code retains its original formatting. That is done by selecting the code and then clicking on the "Code" button above the question input area.
Also, the better way to do this is to use a DocumentFilter, not a KeyListener then you wouldn't have this problem. Read the Swing tutorial which has a working example of how to use a filter.
Edited by: camickr on Feb 20, 2009 9:16 PM