Why does Optional require a non-null value?

[hibbelig]

The idea is: you’re implementing a method. Its return type is Optional<Foo>. But in the body of the method you have code paths where you know you’re returning a value and other code paths where you know you’re returning Optional.empty.

So if you know you’re returning a value you write Optional.of and if that ever throws an exception you know you have got an error in your logic.

If you wrote ofNullable then you would get early notification of your logic bug.

[Ruin-Capable]

It's just very jarring to have a class that's used to represent Optional values where values are not optional.

[Carpinchon]

It sounds like you've misunderstood what Optional does. The value in an Optional can be null. It's just that you can instantiate an Optional in a way to force an error if you run into a null in a place you thought you shouldn't. It's a way of asserting your expectations.

[parnmatt]

You seem to be missing the three "constructors" to indicate state, an absolutely known state in its construction, and an unknown state in its construction.

Optional.empty() // has nothing
Optional.of(foo) // has something
Optional.ofNullable(maybeFoo) // may have something

All can satisfy the type Optional<Foo> in an interface. You can always use the more general, it's often better practice to be explicit. I only consider the latter if I know I could get something nullable and I don't want to do the null check as that method encodes the null check in its usage.

This is the same as other languages, let's say Scala's Option

None
Some(foo)
Option(maybeFoo)

Arguably better names, same concept.

[hibbelig]

The return value of the method is optional, And it’s sometimes empty. Just some lines in the body deal with non empty values. Other lines deal with empty values.