Java data structure sorted by key

Question

I am trying to store integers in a data structure with a String as the key, an example of what im storing is:

key: "Name1", Int: 123
key: "Name2", Int: 124

I want to be able to insert entries so that they are ordered alphabetically for purposes of easy printing to screen.

So far ive been using:

Dictionary<String,Integer> x = new Hashtable<String,Integer>();
x.put("Name1",123);
x.put("Name2",124);

Enumeration<String> e;
String key;
for(e=x.keys(); e.hasMoreElements();){
    key=e.nextElement();
    System.out.println(key + ": " + x.get(key));
}

This Outputs:

Name2: 124
Name1: 123

Why aren't these in alphabetical order? Is there an alternative to Dictionary that I should know about?

Answer 1

Unless otherwise stated, maps/hashmaps/hashtables/dictionaries/etc. don't have any defined sort ordering. A TreeMap<String, Integer> should work for your purposes; it implements the SortedMap<K, V> interface.

That said, I'm not necessarily convinced you should be picking a data structure just because it makes printing easier.

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Side note: Dictionary and Hashtable are legacy classes which exist primarily for backwards compatibility. New code should generally prefer Map and HashMap for general-purpose key-value data structures.