simple dictionary using radix tree

AmazonDictionary.java

import java.util.LinkedList;

/**
 * Implements a dictionary using a radix tree.
 */


public class AmazonDictionary
{

    /* member variables */
    private Node root = new Node();

    /* tester function */
    public static void main(String[] args)
    {
        AmazonDictionary dict = new AmazonDictionary();

        /* valid input */
        dict.put("card");
        dict.put("carnival");
        dict.put("carnivore");
        dict.put("care");

        /* valid output */
        dict.printWords("car");     // words in tree
        System.out.println();

        dict.printWords("carry");   // no words in tree
        System.out.println();

        /* invalid input */
        System.out.println("Testing invalid input - should throw.");
        //dict.put("c.rd");
        dict.printWords("c.rd");
        
        System.out.println("Should not appear.");
    }


    /* API */
    public AmazonDictionary()
    { }

    public void put(String newWord)
    {
        Node current = root;

        for(char c : newWord.toCharArray()) {
            /* check input */
            int index = (int) c - (int) 'a';
            if ((index < 0) || (index > 26))
                throw new java.lang.ArrayIndexOutOfBoundsException("Invalid character input.");

            /* create new node if needed */
            if(current.next[index] == null) 
                current.next[index] = new Node();

            /* move to that node */
            current = current.next[index];
        }

        current.endword = true;
    }

    public LinkedList<String> getWords(String base)
    {
        LinkedList<String> list = new LinkedList<String>();
        Node current = root;

        /* iterate to get to base */
        for(char c : base.toCharArray()) {
            int index = (int) c - (int) 'a';
            if ((index < 0) || (index > 26))
                throw new java.lang.ArrayIndexOutOfBoundsException("Invalid character input.");

            /* base not found */
            if (current.next[index] == null) return null;
            current = current.next[index];
        }

        /* get words stemming from base */
        StringBuilder sb = new StringBuilder(base);
        search(current, sb, list);
        return list;
    }

    public void printWords(String base)
    {
        LinkedList<String> list = getWords(base);

        System.out.print("Words that start with " + base + ": ");

        if (list == null) {
            System.out.println("0");
            return;
        }

        System.out.println(list.size());

        System.out.println("The words are: ");
        for (String str : list)
            System.out.println(str);

    }

    /* private methods */
    private void search(Node x, StringBuilder sb, LinkedList<String> list)
    {
        /* found complete word */
        if(x.endword) list.push(sb.toString());

        /* iterate through children */
        for(int i = 0; i < 26; i++) {
            if(x.next[i] == null) continue;

            StringBuilder copy = new StringBuilder(sb);

            char c = (char) (i + (int) 'a');
            copy.append(c);

            search(x.next[i], copy, list);
        }
    }
        
    /* private classes */
    private class Node
    {
        private Node[] next = new Node [26];
        private boolean endword = false;

        public Node() 
        { }
    }

}