mammal = cow; // [1] pig = mammal; // [2] Checks OK statically, but now pig holds a Cow. print(pig.oink()); // [3] NoSuchMethodException if we get

mammal = cow; // [1] pig = mammal; // [2] Checks OK statically, but now pig holds a Cow. print(pig.oink()); // [3] NoSuchMethodException if we get this far. As far as I understand this means that no precondition can be encoded in the variable type. A function with a Pig argument can still cause a NoSuchMethodException exception because the argument can actually hold a Cow instance.