Java: Error in focusLost method when extract data from the text field

Question

I get this strange error when I try to extract data from a text field on focusLost.

So I have a text-field and the idea is that when user enters data after that clicks somewhere else, the input has to be validated.

this is the line in constructor where I add ficus listener to the text field

ip_address_textField.addFocusListener(new ip_address_textField_FieldHandler());

inside of this class I have another class

public class ip_address_textField_FieldHandler implements FocusListener {

private static final String IPADDRESS_PATTERN =
        "^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
        "([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
        "([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
        "([01]?\\d\\d?|2[0-4]\\d|25[0-5])$";

private Pattern pattern;
private Matcher matcher;

@Override
public void focusGained(FocusEvent e) {
    // TODO Auto-generated method stub
    System.out.println("Focus Gained");

}

@Override
public void focusLost(FocusEvent e) {
    // TODO Auto-generated method stub

    System.out.println(ip_address_textField.getText().trim());
    //ip_address_textField.setText(IPADDRESS_PATTERN);
    System.out.println("Focus Lost ->");
}

The JTextField is class variable

The error which I get is:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at mia.recommender.ch02.Course_Recommender$ip_address_textField_FieldHandler.focusLost

Answer 1

Either of these two is null :

• ip_address_textField - While you try to call getText() it throws nullpointer
• ip_address_textField.getText() - While you try to trim it throws nullpointer