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?

You're looking for a TreeMap

Brian Roach
– Brian Roach

2013-06-22 19:26:20 +00:00
Commented Jun 22, 2013 at 19:26 — Brian Roach
– Brian Roach, Commented Jun 22, 2013 at 19:26
possible duplicate of Java Ordered Map

Brian Roach
– Brian Roach

2013-06-22 19:27:05 +00:00
Commented Jun 22, 2013 at 19:27 — Brian Roach
– Brian Roach, Commented Jun 22, 2013 at 19:27

Matt Ball · Accepted Answer · 2013-06-22 19:26:02Z

4

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.

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.

answered Jun 22, 2013 at 19:26

Matt Ball

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3 Comments

C. K. Young Over a year ago

You should mention the SortedMap and NavigableMap interfaces, which do specify an ordering.

Eduardo Over a year ago

Printing isnt the only reason, i need it to overwrite duplicate entries too, im fairly sure most of the maps do that though

Matt Ball Over a year ago

@clairharrison correct - any correct implementation of Map will prohibit duplicate keys.

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