Java 9 - Optional Additions

In Java 8, the java.util.Optional class was introduced (JavaDoc) as a way to define method return types where there is a need to return no result, and where null is not a good fit as it needs to be explicitly mentioned that an empty return value is indeed possible.

In this article we will have a look at the Optional methods which were added with Java 9.

Hint: in case you wonder about the method references in this article, it is using the method reference syntax from Java 8. In the code examples, we use jshell, a new command-line tool being part of Java 9 JDK.


Optional::ifPresentOrElse is used on Optional instances to execute a lambda being a java.util.function.Consumer if the value exists, or a Runnable - or so-called empty action - if the value does not exist.

jshell> Optional<String> optString = Optional.of("test")
jshell> optString.ifPresentOrElse(s -> System.out.println(s), () -> System.out.println("not there"))

In the code snippet from above, the first lamda defines the Consumer implementation which prints out the given String argument to stdout. The second lamda defines the Runnable implementation without an argument.


The use-case for Optional::or should be relatively self-explanatory. If called on an Optional, it returns the optional itself if its value exists or the Optional created by the given java.util.function.Supplier function (JavaDoc).

jshell> Optional<String> optString = Optional.of("test")
jshell> optString.or(() -> Optional.of("42"))
$3 ==> Optional[test]

The code snippet above in fact does not use the given Supplier function which would return Optional.of("42").

As the return type of or is an Optional, it’s perfectly valid to chain multipe or calls:

jshell> Optional.empty().
   ...> or(() -> Optional.empty()).
   ...> or(() -> Optional.of("42"))
$6 ==> Optional[42]


The stream method is the most useful addition (imho). If a value is present, it returns a instance containing only the optional value.

jshell> Optional<String> optString = Optional.of("test")
jshell> -> System.out.println(elem));

Maybe its usefulness might not be visible at first sight, however, when dealing with Stream-typed return values it indeed makes sense to return a Stream either based on an Optional or on any other Stream implementation.


In this article we showed the latest additions to java.util.Optional in JDK 9, the most useful addition being the new Optional::stream method.