Hacker News Reader

Reminds me of a joke in a John Meaney novel, a physicist discovers faster-than-light travel through a dimension with unusual properties, gaining inspiration from Java's booleans having three states (true, false and NullPointerException).

View on HN

Hate to point it out, but java booleans can only be true or false. Booleans (capital B) can be true, false or null.

Method that is declared as only ever returning bool can also raise any exception that is an instance of java.lang.RuntimeException (which includes NullPointerException) this somewhat bizzare design which combines unchecked and checked exceptions is a source of major discussions since at least late 90's and has much to do with the current concept of null-safety.

final Boolean foo = True

…

if (foo.booleanValue()) { }

Can also NPE.

It can also raise Errors. I know because this one really poorly designed library I used would raise Errors when asking it to decode certain invalid files.

Yeah, but using a raw boolean or Boolean is not considered good practice. They’re up to at least four states now:

null, None, Some(TRUE) and Some(FALSE)

Of course, if you want more than that, you can have unboundedly many by invoking new Boolean(), which guarantees its return value is unique according to ==

Reply on news.ycombinator.com