The following code compiles even if it shouldn't:

1)

class Foo<X> {
 X x;
}

class Test {
   void m(int i) { }

   void test(Foo<? extends Integer> fi) {
      m(fi.x);
   }
}

2)

class Test<T extends Integer> {
  void i(int arg) {}
  void foo(T arg) { i(arg); }
}

3)

class CaptureTest {
  <T> List<T> singleton(T arg) { return null; }
  
  void test(List<? extends Number> l) {
    List<Number> ln = singleton(l.get(0));
  }

}