title: Space Efficient Representation of a Graph in Java?
body: <p>I want to have an undirected graph where the nodes are labelled with a pair (currently using String[] for this) and can be arbitraryly linked to other nodes.  I have started with the type Hashtable.  It turns out that this is not space efficient enough for me - I intend on having around 60,000 nodes (eventually, well in excess of that number).</p>
  
  <p>How should I implement this kind of graph so as to be more memory efficient?  Should I, instead, be considering some kind of Relational Database?</p>