Cascading Generic Type declarations in Java

Question

I am having a hard time finding this anywhere if this is a common problem but I am dealing with what is essentially a cascading type problem.

public class Graph<E> {

    private LinkedList<Node<E>> nodes;

    public Graph() {
        this.nodes = new LinkedList<>();
    }

    public E[] getNodes() {
        ArrayList<E> list = new ArrayList<>();
        for (Node<E> node : nodes)
            list.add(node.getObject());
        return list.toArray(new E[0]); // any way to make this line work?
    }

    // other important stuff
}

I want to do something like this, however I can't instantiate the generic array this way. Where the getNodes() returns the content of the Nodes, not the Nodes themselves, but I can't figure out how.

I was thinking that the Node generic being defined by the Graph generic would mean that the Node class always has the same type as the Graph class. Is that not the case?

The Node class looks like

public class Node<E> {

    private LinkedList<Edge> edges;
    private E obj;

    public E getObject() {
        return obj;
    }

    // other useful stuff
} 

Thanks for any help!

EDIT: all that is needed now is to make the returned Array of the right type. Is there a way to get an Array from an ArrayList that has a generic type assignment?

Answer 1

Someone else came up with an answer that did not work but gave me an idea that ended up working, but they also put it in the comments section of the question so I will reiterate here and answer my own question.

This code works to solve the problem. I more or less lifted the logic from the ArrayList source code for their toArray(E[] a) function (with some of the meat of it cut out of course).

@SuppressWarnings("unchecked")
public E[] getNodes(E[] a) {
    int size = nodes.size();
    // creates an empty array of the right size and type
    E[] arr =(E[]) java.lang.reflect.Array
            .newInstance(a.getClass().getComponentType(), size);
    // fills that array with the correct data
    for (int i = 0; i < size; i++)
        arr[i] = nodes.get(i).getObject();
    return arr;
}

Look at the ArrayList source code in order to see some logic that goes a step farther and accomplishes the same task in a way that is also Thread safe.