Using a runtime exception is like another less readable way to do exactly that.
It's both less and more readable.Its less readable in that its implicit in the code, rather than explicit. But its probably the case that the exception thrown implicitly will be more informative to the user than the hand-written one, which is usually:
default: throw new AssertionError("can't get here");
Which is less readable for the poor fellow who had to debug it.
