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SCJP 5.0 - Generics Mock Exam - 2

3)Which call(s) to method(addandDisp) are error free?

public static <T> void addandDisp(Collection<T> cs, T t)
{
	for (T o : cs)
	{
		s.add(o);
	}
	for (T o : cs)
	{
		System.out.println(o);
	}
}

//call 1
List<? super Object> ls1 = new LinkedList<Object>();
addandDisp(ls1,new String());

//call 2
List<? extends Object> ls2 = new LinkedList<Object>();
addandDisp(ls2,new Object());

//call 3
List<Object> ls3 = new LinkedList<Object>();
addandDisp(ls3,new String());

//call 4
List<? super Object> ls4 = new LinkedList<Object>();
addandDisp(ls4,new Object());

a)only 3
b)only 1 and 3
c)only 1 and 4
d)only 1,2 and 3
e)only 1,3 and 4

Answer:

3)e)
(call 2)Method call 2 cannot work,because the compiler cannot gurantee the type to substitute.But in all other calls it is guranteed.

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