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Better Null-Checking in Java

scottshipp on January 11, 2019

Photo by Estée Janssens on Unsplash Java runs some of the largest sites and platforms in the world but I’ve often struggled with its design as a l...

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Evan Oman • Jan 11 '19 • Edited

How is your Nullable example different than using Option.ofNullable?

String zipCode = Optional.ofNullable(user)
                   .map(User::addresses)
                   .map(UserAddresses::billingAddress)
                   .map(Address::zipCode)
                   .orElse("..."); // or .orElse(null) or .get() w/ exception handling

Evan Oman • Jan 11 '19

Ahh, I missed the intermediary null checks, this is more accurate:

String zipCode = Optional.ofNullable(user)
                   .flatMap(user -> Optional.ofNullable(user.addresses()))
                   .flatMap(addresses -> Optional.ofNullable(addresses.billingAddress())
                   .flatMap(address -> Optional.ofNullable(address.zipCode())
                   .orElse("...");

Grzegorz Ziemonski • Jan 11 '19

No, you didn’t. You can do it exactly as in your first example.

Réda Housni Alaoui • Jan 13 '19

I confirm, the first example works.

But besidd that, this goes against rule of Demeter.

You should not have to access so many indirect attributes to get the zip code. User should expose a getZipCode method.

Eiríkur Ernir Þorsteinsson • Jan 12 '19

Tip: the first case, where null checks are used to handle resources, can usually be avoided by using a try-with-resources statement, available since Java 7. An example is available in the preceding section of the Java tutorial that is linked.

Ondrej • Jan 12 '19

Nice post, mill is IMHO super useful library for Java programmers (for those who did not switch to Kotlin yet or maintaining legacy code written in Java :)).

Jon Bristow • Feb 14 '19

I’m of the opinion that if you can’t sell switching to Haskell, then push for kotlin. It just makes writing JVM code more sane.

The only wackiness comes when you run into a library that is cheating with reflection to overcome the lack of sum or product types in Java. (I’M LOOKING AT YOU, GREMLIN!)

Ondrej • Feb 15 '19

Ha, nice point, Jon,

to be fair, I have to admit that I'm Kotlin enthusiast...but still write much of my code in Java because of.....just because. I have a reasons for it.

HS • May 12 '19

And why not Groovy or Scala instead of Kotlin? TIOBE index shows Groovy(17 today used to be way below) getting way above Kotlin nowadays while the Kotlin gets lower (39 used to be about 35 I think).

Also I played with Kotiln and dislike it as do some other people that use JVM stuff not only me, so why would you assume Kotlin would be better choice?

I really need someone to explain to me what's so great about this language that Groovy or Scala couldn't provide. The only thing is Google and Android in my opinion.

HS • May 12 '19

Nice lib. I do miss ?. and ?? from C# in Java. But I also miss Micronaut/Spring in C# so it's a no brainer :D. Although good thing about JVM frameworks I can combine Groovy and Kotlin with Java to make some stuff have those operators :D.

Christian • Apr 9 • Edited

One way of handling nulls which wasn't discussed is to use the following statics used to check objects before operating on them:

Objects.requireNonNull
Objects.requireNonNullElse
Objects.requireNonNullElseGet

I use them early to fail fast if need be, and we can learn more about the exception by adding a second parameter to Objects.requireNonNullto give context.

docs.oracle.com/javase%2F9%2Fdocs%...

There are also the many @notnull annotations available from various libraries such as Spring.