Javadoc (b116) lacks @FunctionalInterface on Observer signature

Brian Goetz brian.goetz at
Fri Nov 22 09:52:53 PST 2013

> I still have no idea how the annotation is supposed to help us. Can
> anyone provide a concrete use case for @FunctionalInterface?

It captures design intent; the compiler assists you by enforcing that 
design intent (erroring if the class has more than one abstract method.) 
  Like the @Override annotation.

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