Right way to use the @NonNull annotation in Android Studio

Question

I'd like to use the @NonNull annotation in Android, but I can't figure out just the right way to do it. I propose you this example:

public void doStuff(@NonNull String s){      //do work with s...     } 

So when i call doStuff(null) the IDE will give me a warning. The problem is that I cannot rely on this annotation since, like this question points out, they don't propagate very far. So I'd like to put a null check on my method, like this:

 if(s==null) throw new IllegalAgrumentException(); 

But the IDE, assuming that s!=null, will warn me that s==null is always false. I'd like to know what is the best way to do this.

I personally think that there should be an annotation like @ShouldntBeNull that only checks and warns that null isn't passed to it, but doesn't complains when the value is null checked.

Answer 1

You can use Objects.requireNonNull for that. It will do the check internally (so the IDE will not show a warning on your function) and raise a NullPointerException when the parameter is null:

public MyMethod(@NonNull Context pContext) {     Objects.requireNonNull(pContext);     ... } 

If you want to throw another exception or use API level < 19, then you can just make your own helper-class to implement the same check. e.g.

public class Check {     public static <T> T requireNonNull(T obj) {         if (obj == null)             throw new IllegalArgumentException();         return obj;     } } 

and use it like so:

public MyMethod(@NonNull Context pContext) {     Check.requireNonNull(pContext);     ... }