import java.awt.BorderLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.WindowConstants;


public class PeerNPE {

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        JTextField textField = new JTextField();
        JButton button = new JButton("Set read-only");
        
        button.addMouseListener(
            new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    textField.setEditable(false);
                }
            }
        );
        
        frame.getContentPane().setLayout(new BorderLayout());
        frame.getContentPane().add(textField, BorderLayout.CENTER);
        frame.getContentPane().add(button, BorderLayout.SOUTH);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }
}