== Why is this an issue?

The Spring framework provides the annotation `Async` to mark a method (or all methods of a type) as a candidate for asynchronous execution.

Asynchronous methods do not necessarily, by their nature, return the result of their calculation immediately.
Hence, it is unexpected and in clear breach of the `Async` contract for such methods to have a return type that is neither `void` nor a `Future` type.

== How to fix it

Use `void` as the return type if the method is not expected to return a result.
Otherwise, a `Future` should be returned, allowing the caller to retrieve the result once it is ready.
It is permitted to return more specific subtypes that inherit from `Future`.

=== Code examples

==== Noncompliant code example

[source,java,diff-id=1,diff-type=noncompliant]
----
@Async
public String asyncMethod() {
  ...
}
----

==== Compliant solution

[source,java,diff-id=1,diff-type=compliant]
----
@Async
public Future<String> asyncMethod() {
  ...
}
----

Alternatively, if the method does not need to return a result:

[source,java]
----
@Async
public void asyncMethod() {
  ...
}
----

== Resources
=== Documentation
* Spring Framework Documentation - https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Async.html[Annotation Interface Async]