Question

I’m struggling with in combining the visitor and the composite patterns in Java.

I have an Element interface for the Composite. It only has the accept method.

I have an abstract class Composite to handle the child management function(add, remove and getChild). I would like to define the acccept method in the compiste class to avoid having to do it in each subclass. Is there a way to do that?

public abstract class Composite implements Element {

    protected List<Element> elements;

    public Composite() {
        elements = new ArrayList<Element>();
    }

    public void add(Element e) {
     elements.add(e);   
    }

    public void remove(Element e) {
        elements.remove(e);
    }

    public Element getChild(int i) {
        return elements.get(i);
    }

}

Answer 1

Isn’t this what you are looking for?

public abstract class Composite implements Element {

    protected List<Element> elements;

    public void accept(Visitor visitor) {
        for(Element element: elements) {
            element.accept(visitor);
        }
    }

}