Question

Are there any patterns which are similar to Groovy’s safe navigation operator? This is where a null value does make sense and allowing a NullPointerException to be thrown would be wrong.

Other than checking for null, what are some other options? The String class provides a static method to dereference possibly null values but there doesn’t seem to be much use of this pattern apart from the Objects class. Google’s Guava project does have an Optional class but that requires the caller supplying a default which seems too much compared to the safe navigation operator and when you would just want it to be null most of the time. Something that looks like this:

com.google.common.base.Optional.of(fooBar).
    or(org.mockito.Mockito.mock(FooBar.class));

The null object pattern or the option monad in Scala are not what I’m looking for or proposals of adding such operators into future versions of Java, I’m looking for patterns that can be applied in Java now.

Answer 1

The “safe” navigation operator is in my opinion a really bad idea since it supresses exceptions and allows developers to get away with error-ridden code.

There are basically just three cases to consider:

• If you have a null where it is not supposed to be then you have an error and should fail fast and loud. A NullPointerException is a perfectly good way to do this, although some would argue that you should have tests which detected the stray null earlier. Note that Fail-Fast is a very important principle in building robust systems, so you should learn to love your NullPointerExceptions. They are there to guide you to building better software. You should fix the NPE by fixing your code, not by ignoring / suppressing it!
• If a null is allowed but requires specific handling (e.g. a default value) then you should be explicit about this in your code. It’s perfectly good practice to write an if/else null check for this, or else you can use a helper function that itself handles the null case.
• If a null is allowed but requires no specific handling then you don’t need to do anything. Just pass it round as usual.