One question from javabeat.net
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());
Which call(s) to above method(addandDisp) are error free?
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 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.
My doubt is how we can add String in call1.
