A monk asked Java master Kaimu: What is the “single-responsibility principle”? Said Kaimu: That a class shall do exactly one thing, and do it completely. T

A monk asked Java master Kaimu: What is the “single-responsibility principle”? Said Kaimu: That a class shall do exactly one thing, and do it completely. The monk asked: How shall I decide this “one thing”? Said Kaimu: The Fisherman does not build ships, or we would call him a Shipwright. The monk asked: Is there no room in your philosophy for interfaces? What if my class can serve as a Fisherman, and a Shipwright and Sailor besides? Said Kaimu: What would you name such a three-headed monster? The monk replied: Shísho, after my uncle. He lives by the sea and does all these things. Said Kaimu: I would give your class Shísho three instance variables: a Fisherman, a Shipwright, and a Sailor. Then Shísho may implement those interfaces by delegation. The monk replied: I speak of inheritance, yet you answer in composition. All of my uncle is a Fisherman, not just his left foot. What use are objects, if we do not faithfully model the world? Said Kaimu: If I paint a fine shark upon this page, will you say, “Fine shark!” or will you complain that it is flat and does not eat you? The monk asked: But how are we to know when the flat shark is shark enough? Or when our uncle should fish with his left foot? Said Kaimu: Learning how is our “single reponsibility”. - “Flat Shark” http://thecodelesscode.com/case/175 http://thecodelesscode.com/case/175