Suggested Homework #8 (for Quiz #8 on 12/14/07 with Final)

Consider the Java code below: 

interface A {
  void m(A y);
}

interface C extends A {
  A n(C y);
}

class B implements A {
  int x;
  void m(A y){
    return;
  }
}

class D extends B {
  int y;
}

class E extends B implements C {
  A n(C z){
    return z;
  }
}
(a) Name the types, classes, and interfaces that have been created.
(b) Using the notion of structural subtyping which of the following is true ? 
	(i) 	A <: B
	(ii)	A <: C
	(iii)  	B <: A
	(iv)    D <: C
	(v)     D <: B
	(vi)    E <: C
	(vii)   E <: B
	(viii)	E <: A

(c) Which of the following is true ?
  1. A inherits from B
  2. A inherits from C
  3. B inherits from A
  4. D inherits from C
  5. D inherits from B
  6. E inherits from C
  7. E inherits from B
  8. E inherits from A

(d) Which of the following methods typecheck ? 

	  (i)    void fa(A x){ x.m(x); };


	 (ii)    void fb(B x){ x.n(x); };


	(iii)    void fc(C x){ x.n(x); };

(e) Suppose that there were methods fa,fb,fc with the signatures shown in part (d). Which of the following pieces of code typecheck ? Explain. 

    (i) 	A a = A();
	 	fa(a);



   (ii)	        B b = B();
		fa(b);



  (iii)	        B b = B();
		fc(b);



   (iv)	        D d = D();
		fa(d);



    (v)	        D d = D();
		fa(d);
		fb(d);
		fc(d);



   (vi)	        E e = E();
		fa(e);
		fb(e);
		fc(e);