How weak and soft reference work http://www.javaspecialists.co.za/archive/Issue098.html http://javarevisited.blogspot.com.au/2014/03/difference-between-weakreference-vs-softreference-phantom-strong-reference-java.html

Issue about weakhashmap - http://blogs.azulsystems.com/cliff/2007/08/why-weakhashmap.html

When soft reference clean? - http://jeremymanson.blogspot.com/2009/07/how-hotspot-decides-to-clear_07.html