Should I throw a NullPointerException explicitly or let Java do it for me?

Question

As the title says, I am wondering what the best practice is regarding the throwing of NullPointerExceptions. Specifically, if I have an external library function that can return

Answer 1

I dont like having null be a valid return value, even in "exceptional circumstances". So I take yet another approach.

In your case I'd annotate the method createSynthesizer(...) with @NotNull (@NotNull is an amazing annotation). Instead of an NPE, I'd get an IllegalStateException as soon as createSynthesizer(...) would want to return null.

You'd get a:

java.lang.IllegalStateException: @NotNull method .../.../createSynthetiser(...) must not return null

There are several benefits to this approach:

• both NullPointerException and IllegalStateException extends RuntimeException so you're not fundamentally changing your program

• the exception shall be thrown immediately where the error happens (not later on, once you either check/throw yourself or once you try to dereference null)

• you don't need to bother writing the if ... == null / throw part anymore.

As a, gigantic, added benefit some IDE (like IntelliJ IDEA) will warn you in real-time about probable @NotNull violations.