What?

An alternative to java.util.Optional.

Why?

• Allows instances to contain null (map is fully monadic)
• Provides initialization methods for both possible null-handling behaviors (maybe and someNullable)
• Instances are serializable
• Provides specialized instances for all eight primitive types
• Primitive instances are cached for small values
• Has some nice convenience methods not provided by Optional (matches for applying filter + isSome in one operation, and filterTo{Type} for applying filter type checking + map type casting in one operation)

Why not?

• Uses byte code re-writing (enables using a single None instance for both primitive and reference types, and eliminates some ClassCastExceptions in bridged methods)
• Optional is standard and probably good enough
• Will probably be obsoleted by Valhalla

Usage & Examples

some and none

final var some = Option.some(true);
final var none = (BooleanOption) Option.<Boolean>none();
assert some.booleanOrElse(false) == true;
assert none.booleanOrElse(false) == false;

map

assert Option.some(0).mapInt(i -> i == 0 ? null : (Integer) i).get() == null;

filterToType

final var some = Option.some(123);
assert some.filterToType(Object.class).orElse("ABC").equals(123);
assert some.filterToType(String.class).orElse("ABC").equals("ABC");

Caching

assert Option.some(1) == Option.some(1);

Interop with Optional

assert Option.some(123).toOptionalInt().getAsInt() == 123;
assert Option.from(Optional.of("ABC")).get().equals("ABC");

Comparison with Optional

Method	Optional	Option
initialize none	empty	none
initialize non-null -> some	of	some
initialize non-null/null -> some		someNullable
initialize non-null/null -> some/none	ofNullable	maybe
check if value is present	isPresent	isSome
check if value is absent	isEmpty	isNone
action if present	ifPresent	ifSome
action if absent		ifNone
action depending on if present/absent	ifPresentOrElse	ifSomeOrElse
test value		matches
filter value	filter	filter
filter value type		filterToType
map value	map	map
flat map value	flatMap	flatMap
'and' with option		and
'and' with lazy option		andGet
'or' with option		or
'or' with lazy option	or	orGet
get value	get	get
get value or default value	orElse	orElse
get value or lazy default value	orElseGet	orElseGet
get value or throw	orElseThrow	orElseThrow
get value stream	stream	stream

Q & A

What is the difference between maybe and someNullable?

some(value) returns Some[value] if value is not null; otherwise, throws NullPointerException.

maybe(value) returns Some[value] if value is not null; otherwise, returns None.

someNullable(value) returns Some[value] if value is not null; otherwise, returns Some[null].

What is the difference between Option<Boolean> and BooleanOption?

(Applies similarly to other primitive specializations)

Option<Boolean> can be one of four instances: Some[true], Some[false], Some[null], or None.

BooleanOption can be one of three instances: Some[true], Some[false], or None.

filterToBoolean can be used to convert an Option<Boolean> to a BooleanOption. Some[null] will be mapped to None.

BooleanOption can be cast directly to Option<Boolean>.

Any gotchas?

Calling toOptional on Some[null] will throw a NullPointerException because Optional doesn't allow instances to contain null. If desired, use filterToObject to indicate explicitly that Some[null] should be mapped to None before calling toOptional.