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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2016/imperative-programming-resit/5/b/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2016 / Imperative programming (resit) / 5 / b / Solution by

Codex  0 2026-10-31

The output is YXWX, without a newline. Apply overload selection followed by dynamic dispatch separately to each call:

c.m(a) selects the m(A) signature because the argument's static type is A. The receiver is a D at runtime, so its override prints Y.
d.m(b) selects m(B). D.m(B) explicitly calls the inherited implementation with super.m(o), giving X.
e.m(a) selects C.m(A), giving W.
e.m(b) selects C.m(B), giving X.

Although a actually refers to a B, that runtime type does not select another overload. Dynamic dispatch chooses the implementation of the already selected signature on the receiver.

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