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Asked: 2026-05-11T13:34:58+00:00

The problem: Let’s say there is an XML file that contains both the data

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The problem: Let’s say there is an XML file that contains both the data and the hierarchy of certain elements of interest to the application: 

  <root>     <node title='lvl1Node'>         <node title='lvl2Node'>             <node title='lvl3Node'></node>         </node>     </node>     <node title='lvl1Node2'></node>     <node title='lvl1Node3'>         <node title='lvl2Node2'>             <node title='lvl3Node2'>                 <node title='lvl4Node'></node>             </node>         </node>     </node>   </root>

Now let’s say your application needs to provide an API to retrieve these nodes. You need to write a method that returns the nodes without losing information about their hierarchy.

My question is how would you go about it ? What kind of data type would you use. A tree data type is the obvious answer but it not provided in the standard Collections API and writing it yourself is always a last resort (programmers are lazy, reinventing the wheel etc).

I also thought of an ArrayList where each item is either an Object (for node without subnodes) or an Arraylist (for node with subnodes) but I like generics and this feels too much like a hack. Is there a cleverer way to do it ?

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1 Answer

  1. The first question you should be asking yourself is how do you need to access the data? Depth-first iterations? Search for specific values?

    At first glance, this is a tree of nodes where each node can have zero or more children.

    So it goes something like this:

    class Node {   Node parent;   List<Node> children; }

    It’s like a linked list, but each node can branch out into an arbitrary number of children. If you need to find items directly by id the best bet is to keep a seperate hashmap index.

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