HashMap<String, ?> hash1;

HashMap<String, Object> hash2;

public void foobar(Map<String, Object> ms) {
    ...
}

public void foobar(Map<String, ?> ms) {
    ...
}

public void foobar(List<? extends InputStream> ms) {
    ...
}

HashMap<String, ?> hash1;

HashMap<String, ? extends Object> hash1;

int test1(List<?> l) {
  return l.size();
}

int test2(List<Object> l) {
  return l.size();
}

List<?> l1 = Lists.newArrayList();
List<Object> l2 = Lists.newArrayList();
test1(l1);  // compiles because any list will work
test1(l2);  // compiles because any list will work
test2(l1);  // fails because a ? might not be an Object
test2(l2);  // compiled because Object matches Object