Mufid's Code blog

Having Fun with Java's Null

| Comments

So lately i have been diving really deep (or not really) into Java. I found Java’s null is interesting. I think, i hate NullPointerException very much. And most of the time, i hate my own way to deal with those things.

Btw, if you hate compiling Java’s code just to test a one-line command, you may use JavaRepl, which will give you an interactive mode of Java compiler.

String Concatenation

This is interesting. If you run

String result = object + " is cool";

will invoke toString of the object only if the object is not null. If the object is null, toString will not be invoked and it will be replaced with null instead

String result = new Object() + " is cool";
java.lang.Object@55c8a526 is cool

String result = new Object().toString() + " is cool";
java.lang.Object@55c8a526 is cool

String result = null + " is cool";
null is cool

But, you can’t really invoke toString :))

Object o = null;
String result = o.toString() + " is cool";

Object Unboxing

Well, since my code may be executed at another machine, serializing is very usual. And sometimes, i find it is also interesting how Java’s boxing and unboxing work.

This routine will always work:

long l = ...;
Long boxedLong = l;

But how about this?

Long boxedLong = ...;
long l = boxedLong;

Yes, as you might expect, it may throw NullPointerException. Let’s play with it:

long l = (Long) null;

It is not fun. Really. For primitive-in-boxed object, we may want to use itsTypeValue. But in fact, you can’t do that with Long. Meanwhile, you can do that with Boolean.

long l = ((Long) null).longValue();

long l = new Long(null).longValue();
java.lang.NumberFormatException: null

new Boolean(null).booleanValue();

What really happened to those? I don’t know.

if not null and not null

Sometimes, my flawless code merely run into this horrible lengthy operators:

if (provider != null && provider.getGlobalInfo() != null) {
    InfoBase globalInfo = provider.getGlobalInfo();

Well… what if i have something longer than that? Simply add null check before doSomethingWith(that)!

if (provider != null && provider.getProviderCoordinate() != null && provider.getProviderCoordinate().getLatidudeBase() != null ) {
    Coordinate c = provider.getProviderCoordinate().getLatidudeBase();

Well.. still too long. You don’t really need to get into that detail. Take care of your object’s contract. Why don’t we give a default value instead of null?

class ProviderBase {
  InfoBase globalInfo;
  InfoBase getGlobalIInfo() {
    if (globalInfo == null) {
      return InfoFactory.getDefaultInfo();
    return globalInfo;

But still, if null is expected, then handle it with a better way. Just because i hate NPE, it is just better to give default value because most of the time null data is caused by serialization of not-yet-completed data model migration. You might have a better way other than default value (like, Annotation?), but you get the idea.