FutureReturnValueIgnored
Return value of methods returning Future must be checked. Ignoring returned Futures suppresses exceptions thrown from the code that completes the Future.

The problem

Methods that return java.util.concurrent.Future and its subclasses generally indicate errors by returning a future that eventually fails.

If you don’t check the return value of these methods, you will never find out if they threw an exception.

Nested futures can also result in missed cancellation signals or suppressed exceptions - see Avoiding Nested Futures for details.

Suppression

In certain scenarios like tests, there might be a need of not using the future values. One can suppress such false positives by either suppressing the check directly or by saving the future in variables named with prefix unused. For example:

@SuppressWarnings("FutureReturnValueIgnored")
@Test
public void futureInvocation_noMemoryLeak() {
  functionReturningFuture();
}

@Test
public void futureInvocation_noMemoryLeak() {
  Future<?> unusedFuture = functionReturningFuture();
}