IntelliJ null check warnings

Question

I often have code like this:

protected @Nullable Value value;

public boolean hasValue() { return value != null; }

the problem with this is that when I do null checks like so:

if (!hasValue()) throw...
return value.toString();

then IntelliJ will warn me about a possible NPE

whereas

if (value != null) throw...
return value.toString();

avoids this warning.

is there a way to decorate my hasValue() method so that IntelliJ knows it does a null check? and won't display the warning?

what about the `@suppresswarnings( nullcheck )` annotation ? — blurfus, Feb 09 '17 at 01:47
What's the version of Intellij-Idea that you use? My 14th version doesn't show me this warning (in this particular case). — Andremoniy, Feb 09 '17 at 01:56
@Andremoniy It is the 2016.3.4. Oh.. I see the problem I use `@Nullable` to decorate the value field - if I removed that, it goes away. — ycomp, Feb 09 '17 at 02:00
You can use @NotNull to indicate that a parameter should never be null. IntelliJ can add bytecode verification to your method in these cases. — Sam Barnum, Feb 09 '17 at 02:02
@Andremoniy `package org.jetbrains.annotations;` I like to decorate the fields that are set by the constructors with `@Nullable/@NotNull — ycomp, Feb 09 '17 at 02:07
If you're going to throw anyway why go through this rigamarole instead of just letting the NPE go? if it's a violation of contract, that's perfectly fine. — pvg, Feb 09 '17 at 02:07
@pvg better exception message, easily recognizable what happened in the logs (in this case, I don't always do that for all checks - but in this case it `hasValue()` is kind of like an API method) — ycomp, Feb 09 '17 at 02:08
Hardly seems worth the lines of ceremony. Plus if it's happening, it's actually a bug right? so it's not like some condition that requires its own information message. — pvg, Feb 09 '17 at 02:10

score 4 · Accepted Answer · answered Feb 09 '17 at 02:15

Intellij-Jetbrains is very clever IDE and itself suggests you way for solving many problems.

Look at screenshot below. It suggests your five ways for removing this warning:

1) add assert value != null;

2) replace return statement with return value != null ? value.toString() : null;

3) surround with

    if (value != null) {
        return value.toString();
    }

4) suppress inspection for this particular statement by adding commentary:

//noinspection ConstantConditions
return value.toString();

5) add at least, as earlier @ochi suggested use @SuppressWarnings("ConstantConditions") annotation which can be used for method or for whole class.

To invoke this context menu use shortcut keys Alt+Enter (I think they are common for all OS).

All of these techiques indeed prevent IntelliJ from issuing the warning. However, none of them answers the original question of ensuring that "IntelliJ knows it [hasValue] does a null check". Some other tools have more sophisticated code analysis and support a postcondition annotation [`@EnsuresNonNullIf`](https://checkerframework.org/api/org/checkerframework/checker/nullness/qual/EnsuresNonNullIf.html) that does what the original poster asked -- but unfortunately IntelliJ currently does not. — mernst, Feb 10 '17 at 17:02

1 Answers1