I'm wondering why the assert keyword is so underused in Java? I've almost never seen them used, but I think they're a great idea. I certainly much prefer the brevity of:
assert param != null : "Param cannot be null";
to the verbosity of:
if (param == null) {
throw new IllegalArgumentException("Param cannot be null");
}
My suspicion is that they're underused because
- They arrived relatively late (Java 1.4), by which time many people had already established their Java programming style/habit
- They are turned off at runtime by default
Answer
assertions are, in theory, for testing invariants, assumptions that must be true in order for the code to complete properly.
The example shown is testing for valid input, which isn't a typical usage for an assertion because it is, generally, user supplied.
Assertions aren't generally used in production code because there is an overhead and it is assumed that situations where the invariants fail have been caught as coding errors during development and testing.
Your point about them coming "late" to java is also a reason why they aren't more widely seen.
Also, unit testing frameworks allow for some of the need for programmatic assertions to be external to the code being tested.