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tf.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent ke) {
String value = tf.getText();
int l = value.length();
if (ke.getKeyChar() >= '0' && ke.getKeyChar() <= '9'|| ke.getKeyCode()==KeyEvent.VK_BACK_SPACE) {
tf.setEditable(true);
label.setText("");
} else {
tf.setEditable(false);
label.setText("* Enter only numeric digits(0-9)");
}
}
});