4. Avoid creating duplicate objects
5. Eliminate obsolete object references
12. Minimize accesibility of classes and members
21. Replace enum constructs with classes
23. Check parameters for validity
27. Return zero-length arrays, not nulls
29. Minimize the scope of local variables
30. Know and use the libraries
31. Avoid float and double if exact answers are required
32. Avoid strings where other types are more appropriate
33. Beware the performance of string concatenation
36. Use native methods judiciously
37. Optimize judiciously
39. Use exceptions only for exceptional conditions
47. Don’t ignore exceptions