JTextField component = new JTextField(); component.addKeyListener(new MyKeyListener()); public class MyKeyListener extends KeyAdapter { public void keyTyped(KeyEvent evt) { JTextComponent c = (JTextComponent)evt.getSource(); char ch = evt.getKeyChar(); if (Character.isLowerCase(ch)) { try { c.getDocument().insertString( c.getCaretPosition(), ""+Character.toUpperCase(ch), null); evt.consume(); } catch (BadLocationException e) { } } } }