References on Design Patterns
Design Patterns, E. Gamma, J. Vlissides, R. Helm, R. Johnson, 1995, ISBN 0-201-63361-2, Addison Wesley.
Patterns Languages of Program Design 1,2,3, 1995-1998, Addison Wesley.
Patterns in Java I,II,III, Mark Grand, 1998-2000, Addison Wesley.
http://hillside.net/patterns/
http://www.cetus-links.org/oo_patterns.html
http://st-www.cs.uiuc.edu/cgi-bin/wikic/wikic
Free Book : www.patterndepot.com/put/8/JavaPatterns.htm