import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Main {
public static void main(String[] args) {
JTextField tf = new JTextField("mm");
tf.setPreferredSize(tf.getPreferredSize());
tf.setText("");
JPanel pHacked = new JPanel();
pHacked.add(tf);
JPanel pStock = new JPanel();
pStock.add(new JTextField(2));
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new java.awt.GridLayout(0, 1));
frame.add(pHacked);
frame.add(pStock);
frame.setSize(150, 150);
frame.setVisible(true);
tf.requestFocus();
}
}