EffectivelyFinalAndMemberVariables.java

@FunctionalInterface
public interface SimpleFunctionalInterface {
    public int returnAnswerToUltimateQuestion();
}

    @Test
    public void normalInterfaceOnlyOneAbstractMethod() {

        int x = 1;

        SimpleFunctionalInterface myInterfaceImpl = () -> {
//            x = 2; // impossible
            instanz = 3; // possible because member variables are copied when creating lambdas. (http://stackoverflow.com/questions/25055392/lambdas-local-variables-need-final-instance-variables-dont)
            
          // TODO: Why is the class, in which the lambda is defined, copied? I thought that lambdas are "closed" definitions of functionality that can be passed around.
            return 0;
        };
    }

Thanks a lot! Changed my workshop accordingly. Could you please have a look at this commit? It should contain everything important, but a review would be nice. :)