The JLS states in §8.4.9 Overloading:
- When a method is invoked (§15.12), the number of actual arguments (and any explicit type arguments) and the compile-time types of the arguments are used, at compile time, to determine the signature of the method that will be invoked (§15.12.2).
- If the method that is to be invoked is an instance method, the actual method to be invoked will be determined at run time, using dynamic method lookup (§15.12.4).
So in your case:
- The method argument (
this
) is of compile-time typeParent
, and so the methodprint(Parent)
is invoked. - If the
Worker
class was subclassed and the subclass would override that method, and theworker
instance was of that subclass, then the overridden method would be invoked.
Double dispatch does not exist in Java. You have to simulate it, e.g. by using the Visitor Pattern. In this pattern, basically, each subclass implements an accept
method and calls the visitor with this
as argument, and this
has as compile-time type that subclass, so the desired method overloading is used.