Re: Table object

markspace <>
Fri, 17 Jul 2009 18:49:27 -0700
Philipp wrote:

I'm looking for a collection which behaves like a two column table
(ordered key - value pairs, key not unique). Is there such a thing
either in the JRE or Apache collections?

Hmm, the basic 2D table is called an array:

   Type[][] table = ...;

The improved version of that is a List, typically an ArrayList:

   ArrayList<type[]> table = ...;

Neither one is inherently sorted however. There are sort methods you
can call in Arrays and Collections

TreeMap seems like the closest match out of the older Java 5 collections:

   TreeMap< Type1, Type2 > = ...;

But I think that's been gainsaid in this discussion already. There is
an IdentityHashMap, but that's unsorted. Bummer, it looks like you may
have to roll your own. Let's see how close I can get to what the other
posters did:

..... much later... OK I needed my IDE to finish this, and basically I
came up with a TreeMap too. The following code could stand to return
unmodifiable lists, as Lew pointed out. And I'm a little shaky on that
K extends Comparable... I think there should be a "? super" in there.
Have to give it some more thought. Seems to work ok though:

package fubar;

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;

  * @author Brenden
public class SortedMultiMap<K extends Comparable,V> extends
AbstractMap<K,List<V>> {

     Map<K,List<V>> map = new TreeMap<K,List<V>>();

     public Set<Entry<K, List<V>>> entrySet()
         return map.entrySet();

     public List<V> get( Object key )
         return map.get( key );

     public List<V> put( K key, V value )
         List<V> exists = map.get( key );
         if( exists != null ) {
             exists.add( value );
         } else {
             exists = new ArrayList<V>();
             exists.add( value );
             map.put( key, exists );
         return exists;

     public List<V> remove( Object key )
         return map.remove( key );

     public String toString()
         return map.toString();

     public static void main( String[] args )
         // test harness
         SortedMultiMap<String,String> kills =
                 new SortedMultiMap<String,String>();
         kills.put( "Blossuom", "Mojo Jojo");
         kills.put( "Butercup", "Mojo Jojo");
         kills.put( "Bubbles", "Gangreen Gang");
         kills.put( "Butercup", "The Amoeba Boys");
         kills.put( "Bubbles", "Sedusa");
         kills.put( "Blossuom", "Fuzzy Lumpkins");

         for( Entry<String,List<String>> e : kills.entrySet() ) {
             System.out.println( e.getKey() + e.getValue() );

         System.out.println( kills );

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