Implement Tree Datastructure in Java

Question

Is there a good available data structure to represent a tree in Java?

Specifically, these are the representational parameters

• At any node may have an arbitrary number of children
• Each node is a String having a String child only
• Able to get all the children given an input string representing a given node

Answer 1

I wrote a small "TreeMap" class based on "HashMap" that supports adding paths:

import java.util.HashMap;
import java.util.LinkedList;

public class TreeMap<T> extends LinkedHashMap<T, TreeMap<T>> {
    public void put(T[] path) {
       LinkedList<T> list = new LinkedList<>();
       for (T key : path) {
            list.add(key);
       }
       return put(list);
   }

    public void put(LinkedList<T> path) {
       if (path.isEmpty()) {
           return;
       }
        T key= path.removeFirst();
       TreeMap<T> val = get(key);
       if (val == null) {
            val= new TreeMap<>();
            put(key, val);
       }
        val.put(path);
   }
}

It can be use to store a Tree of things of type "T" (generic), but does not (yet) support storing extra data in it's nodes. If you have a file like this:

root, child 1
root, child 1, child 1a
root, child 1, child 1b
root, child 2
root, child 3, child 3a

Then you can make it a tree by adding this code

TreeMap<String> root = new TreeMap<>();
Scanner sc = new Scanner(new File("input.txt"));
while (sc.hasNextLine()) {
  root.put(sc.nextLine().split(", "));
}

You can easily adapt to this tree