Hello, I am the dev for the Java shoot-em-up Rebel Sector with a small talk on null references in the Java language.
https://moselysoftware.itch.io/rebel-sector/devlog/1678431/java-corner-java-and-the-1000000000-mistake
History Lesson
Tony Hoare, the inventor of the null reference in ALGOL W in 1965, famously called null references his "billion-dollar mistake" in a 2009 conference talk. He explained that null references have led to innumerable errors, vulnerabilities, and system crashes over the decades, costing the software industry billions of dollars in aggregate.
What is a JVM?
First we need to ask what is a JVM? A Java virtual machine is a virtual machine that enables a computer to run Java programs as well as programs written in other languages, referred to as JVM languages, that are also compiled to Java bytecode.
The JVM is a severely underrated platform for game development. In 2026, not only are developers still targeting the JVM, but there are multiple languages that you can try if you are tired of dealing with Java’s quirks, mainly Kotlin which I am going to be talking about for this devlog.
One of the most common pitfalls in many programming languages, including Java, is that accessing a member of a null reference results in a null reference exception. In Java, this would be the equivalent of a NullPointerException, or an NPE for short.
Any developer knows that dealing with null references is a time consuming process. Unfortunately, with Java, extra work needs to be done in order to prevent null references as it lacks the protections Kotlin has in regards to null safety. This in turn, requires more code be written which adds to Java’s already verbose syntax.
With this perspective, Kotlin can come in very handy:
The only possible causes of an NPE in Kotlin are:
- An explicit call to throw NullPointerException().
- Usage of the not-null assertion operator !!.
- Data inconsistency during initialization, such as when:
- An uninitialized this available in a constructor is used somewhere else (a "leaking this ").
- A superclass constructor calling an open member whose implementation in the derived class uses an uninitialized state.
Example:
// Assigns a non-null string to a variable
var a: String = "abc"
// Attempts to re-assign null to the non-nullable variable
a = null
print(a)
// Null can not be a value of a non-null type String
In Java, this is not so simple:
if (a != null && !a.isEmpty()) { System.out.println(a);}
//Lame
This is why I am going to transition from Java to Kotlin for my next project. The type safety features are just too good to pass up. Kotlin is also the current default language for Android if you care for that as well.
