How to instantiate a generic recursive class in Java

Question

My problem is that I am using a class not developed by me (I took it from Microsoft Azure SDK for Java). The class is called Node and you can see it here.

As you can see the class is a generic class declared recursively like this:

public class Node<DataT, NodeT extends Node<DataT, NodeT>> {
      ...
}

When I try to instantiate it I don't know how to do it. I am doing this but I know IT IS NOT the way because it has no end:

Node<String, Node<String, Node<String, Node<...>>>> myNode = new Node<String, Node<String, Node<String, Node<...>>>>;

I hope you understand my question. Thanks.

@ArneBurmeister Exactly my point! It doesn't help at all that the Node class is not abstract. — fps
– fps, Commented May 11, 2017 at 0:54

Harmlezz · Accepted Answer · 2017-05-10 13:21:28Z

5

One way is to extend Node like:

class MyNode<T> extends Node<T, MyNode<T>> {
}

and then instantiate it like:

Node<String, MyNode<String>> node1 = new MyNode<String>();

or

MyNode<Integer> node2 = new MyNode<Integer>();

answered May 10, 2017 at 13:21

Harmlezz

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1 Comment

davidxxx Over a year ago

Fine and flexible way.

Radiodef · Accepted Answer · 2017-05-10 13:19:53Z

4

You have to declare a class which extends Node so you can use the name of the class:

class StringNode extends Node<String, StringNode> {
}

answered May 10, 2017 at 13:19

Radiodef

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Comments

khelwood · Accepted Answer · 2017-05-10 13:25:24Z

2

You can use a wildcard in your variable declaration:

Node<String, ?> n = new Node<>();

Or you can create an explicit subclass

class StringNode extends Node<String, StringNode> { }

and instantiate it via

Node<String, ?> n = new StringNode();

or

StringNode n = new StringNode();

answered May 10, 2017 at 13:25

khelwood

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