How can I avoid NullPointerException warning in this Java lambda expression code?

Question

How can I avoid NullPointerException warning in this Java code? I am working with IntelliJ and I am getting this warning:

Method Invocation 'getChartController()' may produce 'java.Lang.NullPointerException'"

chartControlButtons.add(
    new JButton("Zoom In") {{
        addActionListener(
            (ActionEvent e) -> getChartController().zoomIn()
        );
    }}
);

How about you just check for null getChartController() before lambda expression? Or you could check null inside it as well. — Shanu Gupta, Apr 20 '18 at 06:29
you can add a try catch block around that statement and see what can be done in case of null pointer exception. — pkgajulapalli, Apr 20 '18 at 06:31
@pkgajulapalli Is `null` really an exception situation here? — lexicore, Apr 20 '18 at 06:34
Post more of your code. How does `getChartController()` look like? — lexicore, Apr 20 '18 at 06:35
Make `getChartController()` return a [null object](https://en.m.wikipedia.org/wiki/Null_object_pattern) instead of null, such that invoking the method on it does nothing. — Andy Turner, Apr 20 '18 at 06:39
@lexicore As `getChartController()` method may return null, calling `zoomIn` method will throw a null pointer exception, right? — pkgajulapalli, Apr 20 '18 at 08:20
@pkgajulapalli Yes. But how would we know if it can return null or not if you don't post relevant code? — lexicore, Apr 20 '18 at 08:54
Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Martin van Wingerden, Sep 12 '19 at 05:38
@MartinvanWingerden That is not really a duplicate of this question. This question is asking how to fix the static analysis warning that warns the code may produce a NullPointerException. — Mark Rotteveel, Sep 12 '19 at 08:34
@MarkRotteveel The fact is that `getChartController` might return `null` and that is the key to understanding, and an issue which is more a full duplicate (https://stackoverflow.com/questions/48858721/how-can-i-fix-this-method-invocation-isemailverified-may-produce-java-lang) was marked as a duplicate of the question mentioned above. IMHO this question has been asked in many other flavors before, its harder to choose which is the best duplicate then deciding whether its a duplicate :-) — Martin van Wingerden, Sep 12 '19 at 09:53
@MartinvanWingerden The OP in that question is asking about the actual occurrence of a NullPointerException (they even included the stacktrace), and not just about a static analysis warning. — Mark Rotteveel, Sep 12 '19 at 09:56
@MarkRotteveel I linked the wrong one, the one from which I started was https://stackoverflow.com/questions/57208201/cannot-resolve-method-invocation-may-produce-nullpointerexception — Martin van Wingerden, Sep 12 '19 at 10:02

score 1 · Accepted Answer · answered Apr 20 '18 at 06:36

You can use optional to avoid NullPointerExceptions.

Following is a kind of optional use this case.

     chartControlButtons.add(
        new JButton("Zoom In") {{
          addActionListener(
              (ActionEvent e) -> Optional.ofNullable(getChartController()).ifPresent(s -> s.zoomIn())
          );
        }}
    );

How can I avoid NullPointerException warning in this Java lambda expression code?

1 Answers1