package test; 
     
public static void main(String[] args) {

    // Create a visitable collection
    FooCollection c = new FooCollection();

    // Add some members
    c.add(new Foo());
    c.add(new Bar());

    // Visit
    c.accept(new IVisitor<Foo>() {

        public void visit(Foo foo) {
            System.out.println("Foo");
        }

        public void visit(Bar bar) {
            System.out.println("Bar");
        }
    });
}

public static class Foo {
}

public static class Bar extends Foo {
}

public static interface IVisitor<T> {

    public void visit(T object);
}

public static class FooCollection {

    private final ArrayList<Foo> m_list = new ArrayList<>();

    public void accept(IVisitor<Foo> visitor) {
        for (Foo foo : m_list) {
            visitor.visit(foo);
        }
    }

    public void add(Foo foo) {
        m_list.add(foo);
    }
}