What is the reason for these PMD rules?

Thomas_Owens_572 0
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DataflowAnomalyAnalysis: Found 'DD'-anomaly for variable 'variable' (lines 'n1'-'n2').

DataflowAnomalyAnalysis: Found 'DU'-anomaly for variable 'variable' (lines 'n1'-'n2').

DD and DU sound familiar...I want to say in things like testing and analysis relating to weakest pre and post conditions, but I don't remember the specifics.

NullAssignment: Assigning an Object to null is a code smell. Consider refactoring.

Wouldn't setting an object to null assist in garbage collection, if the object is a local object (not used outside of the method)? Or is that a myth?

MethodArgumentCouldBeFinal: Parameter 'param' is not assigned and could be declared final

LocalVariableCouldBeFinal: Local variable 'variable' could be declared final

Are there any advantages to using final parameters and variables?

LooseCoupling: Avoid using implementation types like 'LinkedList'; use the interface instead

If I know that I specifically need a LinkedList, why would I not use one to make my intentions explicitly clear to future developers? It's one thing to return the class that's highest up the class path that makes sense, but why would I not declare my variables to be of the strictest sense?

AvoidSynchronizedAtMethodLevel: Use block level rather than method level synchronization

What advantages does block-level synchronization have over method-level synchronization?

AvoidUsingShortType: Do not use the short type

My first languages were C and C++, but in the Java world, why should I not use the type that best describes my data?

pmd java
6 Answers

Just a note on the final question.

Putting "final" on a variable results in it only be assignable once. This does not necessarily mean that it is easier to write, but it most certainly means that it is easier to read for a future maintainer.

Please consider these points:

  • any variable with a final can be immediately classified in "will not change value while watching".
  • by implication it means that if all variables which will not change are marked with final, then the variables NOT marked with final actually WILL change.

This means that you can see already when reading through the definition part which variables to look out for, as they may change value during the code, and the maintainer can spend his/her efforts better as the code is more readable.

user_538970

What advantages does block-level synchronization have over method-level synchronization? Synchronize a method is like do a synchronize(getClass()) block, and blocks all the class.

Maybe you don't want that

damian_13567090
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