You are using Sequencer which is the name of an interface as an argument to the Sequencer constructor. You can't create an object of Sequencer because (as any interface does) it has only empty methods. I am not familiar with this example, though people do seem to ask questions about it her quite frequently. Go back to the Head First book and see what they say there. They might have another example on the next page where the Sequencer is changed to a class, and you might have to run the two together.