如何将getSource（）转换为JTextField？

Question

I am making a KeyListener class so I can control any JTextField that I want, but I do not know how to get whatever JTextField I call so I can press escape and clear the JTextField ? Here is my current code

private class IntegerTxtListener implements KeyListener {
    public void keyTyped(final KeyEvent e) {
            if (e.getKeyChar() < KeyEvent.VK_0
                    || e.getKeyChar() > KeyEvent.VK_9) {
                e.consume();
            }
        if (e.getKeyChar() == KeyEvent.VK_ESCAPE) {
            e.consume();
           //My Problem is Here----------------------------
            e.getSource()).setText("");
        }
    }

    @Override
    public void keyPressed(KeyEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void keyReleased(KeyEvent arg0) {
        // TODO Auto-generated method stub

    }
}

Answer 1

It looks like, to me, you are trying to create a text field that only allows integer values. First of all, you shouldn't be using a KeyListener for a JTextField . Instead you should be using a DocumentFilter for the underlying document of the JTextField . The DocumentFilter can filter out any unwanted input.

Here is an example of a JTextField that only allows integer input.

private JTextField createTextField() {
    JTextField field = new JTextField();
    ((AbstractDocument) field.getDocument()).setDocumentFilter(new DocumentFilter() {
        @Override
        public void insertString(FilterBypass fb, int off, String str, AttributeSet attr)
                throws BadLocationException {
            fb.insertString(off, str.replaceAll("\\D++", ""), attr);  // remove non-digits
        }

        @Override
        public void replace(FilterBypass fb, int off, int len, String str, AttributeSet attr)
                throws BadLocationException {
            fb.replace(off, len, str.replaceAll("\\D++", ""), attr);  // remove non-digits
        }
    });
    return field;
} 

---

Also, may be unrelated, but another listener you may want to look into, dealing with text input is a DocumentListener , that will listener for changes in the underlying document of the text field. You can read more at How to write DocumentListeners

Answer 2

I don't know what are you trying to achieve but if it is about to control user input consider using a DocumentFilter instead.

If you still want to use a KeyListener just cast e.getSource() to JTextField , to ensure to don't have a ClassCastException you should use instanceof operator like example below.

if(evt.getSource() instanceof JTextField){
   JTextField textfield = (JTextField) e.getSource();
   textfield.setText("..");
   e.consume();
}

Consider extends KeyAdapter rather than implementing KeyListener .

Answer 3

I think this schould work:

if (e.getKeyChar() == KeyEvent.VK_ESCAPE) {
    e.consume();
   //My Problem is Here----------------------------
    ((JTextField)e.getSource()).setText("");
}

Just the default way of casting objects.

But it might happen that some errors occur if e is not an instance of JTextField .
So if you are sure that your Listener will not give a source other than JTextField object you can go this way. Otherwise you you add errorhandling /-prevention.