Java: Why aren't NullPointerExceptions called NullReferenceExceptions?

java

Solution

Java does indeed have pointers--pointers on which you cannot perform pointer arithmetic.

From the venerable JLS:

There are two kinds of types in the Java programming language: primitive types (§4.2) and reference types (§4.3). There are, correspondingly, two kinds of data values that can be stored in variables, passed as arguments, returned by methods, and operated on: primitive values (§4.2) and reference values (§4.3).

And later:

An object is a class instance or an array.

The reference values (often just references) are pointers to these objects, and a special null reference, which refers to no object.

(emphasis theirs)

So, to interpret, if you write:

Object myObj = new Object();

then `myObj` is a reference type which contains a reference value that is itself a pointer to the newly-created `Object`.

Thus if you set `myObj` to `null` you are setting the reference value (aka pointer) to `null`. Hence a NullPointerException is reasonably thrown when the variable is dereferenced.

Don't worry: this topic has been heartily debated before.

Problem

Original source