Software design principals

1. Open source useful tool and frameworks  
2. Tool and techonology refcards 
3. Choosing checked or unchecked user defined exception
4. Static import in java 
5. Coupling

Cohesion - http://en.wikipedia.org/wiki/Cohesion_%28computer_science%29
Cyclomatic Complexity - http://www.javacodegeeks.com/2011/09/measuring-code-complexity.html

Java design patterns - http://www.oodesign.com
Groovy design patterns - http://groovy.codehaus.org/Design+Patterns+with+Groovy 

UML Class diagram - http://www.agilemodeling.com/artifacts/classDiagram.htm
                          http://www.ibm.com/developerworks/rational/library/content/RationalEdge/sep04/bell/

Pros and cons of reflection - http://docs.oracle.com/javase/tutorial/reflect/index.html