A strength of JTransformer is that it capable of doing analysis on the source code and transformations. In this section, we are writing a transformation that could be applied to code found by the System.out.println detector from the "Write your own analysis"-Example.

If you want to learn what Conditional Transformations are and how you can use them (run a ct, run a sequence of cts, examine the results of a ct …) please have a look at this page: Conditional Tranformations. If you need more examples for transformations you can have a look at the Tutorial Project ¹⁾.

The transformation for our System.out.println detector has to replace the call to System.out.println by a call to a logging method. How the logging method can be detected has to be defined in the condition part of the ct.

:- multifile(user:ct/3).     % Dont forget the declaration!

user:ct( replaceSysoutWithLogging(CallId),              % HEAD
    (                                                   % CONDITION
      sysout_analysis:sysout_call(CallId,CallParent, Enclosing, FieldAccess, StaticTypeRef, Argument),
                                                        % Call the analysis predicate and bind all IDs
      get_term(FieldAccess, FieldAccessTerm),           % get the terms which should be deleted
      get_term(StaticTypeRef, StaticTypeRefTerm),
            
      classT(MyLoggerClass, _, 'MyLogger', _, _),       % Get the ID belonging to class 'MyLogger'
      methodT(LoggingMethod, MyLoggerClass, println, _, MethodType, _, _, _),
                                                        % ... and the ID for the logging method

      new_id(NewTypeRef)                                % NewTypeRef is a yet unused ID
    ),
    (                                                   % TRANSFORMATION:
      delete(FieldAccessTerm),                          % delete the field access
      delete(StaticTypeRefTerm),                        % delete the static type reference
      
      replace(callT(CallId, CallParent, Enclosing, NewTypeRef, [Argument], LoggingMethod, [], MethodType))
                                                        % replace the existing callT fact with the new one 
                                                        % (call the logging method instead of System.out.println)
      
      add(staticTypeRefT(NewTypeRef, CallId, Enclosing, MyLoggerClass)),
                                                        % add the static type reference to the class "MyLogger"
    )
).