Multimethods in Groovy

Every time I switch from Groovy to Java I have to remind myself that some things that seem so natural and work as expected in Groovy, don't work in Java. One of such differences is method dispatching. Groovy supports multiple dispatch, while Java does not. Therefore the following code works differently in Groovy and Java:

public class A {
    public void foo(A a) { System.out.println("A/A"); }
    public void foo(B b) { System.out.println("A/B"); }
}
public class B extends A {
    public void foo(A a) { System.out.println("B/A"); }
    public void foo(B b) { System.out.println("B/B"); }
}
public class Main {
    public static void main(String[] args) {
        A a = new A();
        A b = new B();
        a.foo(a);
        b.foo(b);
    }  
}

$ java Main
A/A
B/A

$ groovy Main.groovy
A/A
B/B