Alphabetize a HashMap of Characters

Question

I have a program that takes the number of instances of a character in a string and then puts them into a HashMap. I have it working, but how do I alphabetize the HashMap. Here is my code:

import java.util.*;
import java.lang.*;
import javax.swing.JOptionPane;
import java.io.*;
public class CharacterCount
{
   public static void main(String args[])
   {
      {
      String s = JOptionPane.showInputDialog("Enter in any text.");
      String str = s.replaceAll("[., ]", "");
      String[] splitted = str.split("");
      HashMap hm = new HashMap();

      for (int i = 0; i < splitted.length; i++) {
         if (!hm.containsKey(splitted[i])) {
            hm.put(splitted[i], 1);
         } else {
            hm.put(splitted[i], (Integer) hm.get(splitted[i]) + 1);
            }
      }
      for (Object word : hm.keySet()) {
         if (word.equals("")) {
            System.out.println("Spaces: " + (Integer) hm.get(word));
            }
         else {
            System.out.println(word + ": " + (Integer) hm.get(word));
            }
         }
      }
   }
}

What do I need to add to make it alphabetize/reorganize the HashMap?

You can't alphabetize a HashMap. You *can* extract the entries of a HashMap into an array and sort the array, but a HashMap by definition is unordered. — Hot Licks, Jan 02 '14 at 02:51
Check out http://stackoverflow.com/q/2889777/509840. If you declare it a SortedMap, it will be alphabetized by key. — rajah9, Jan 02 '14 at 02:52

score 2 · Accepted Answer · answered Jan 02 '14 at 02:52

An HashMap is, by default, unsorted. This because its implementation can't rely on order of elements.

If you need a sorted map then you will have to look into a TreeMap which supplies the same interface as a HashMap but it's inherently sorted on keys according to their natural ordering (or a custom Comparator). Mind that a TreeMap doesn't allow ordering on values, so if you need to sort your data by value then you will have to build your own sorted collection.

This is usually done by taking the Map.Entry<K,V> entrySet() and then build a new SortedSet by following your ordering rules.

score 0 · Answer 2 · edited May 23 '17 at 10:32

0

Most maps, including HashMap, make no promises about order of contents. Consider SortedMap, or maintaining both a hash map and a sorted list in parallel.

Difference between HashMap, LinkedHashMap and TreeMap

edited May 23 '17 at 10:32

Community

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answered Jan 02 '14 at 02:54

keshlam

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Alphabetize a HashMap of Characters

2 Answers2