code: public void transform(final IClassTransformer transformer,
                          final String inputDir,
                          final String outputDir) {
      transform(transformer, inputDir, outputDir, iterateClassnames(inputDir));
    }
docs: Search for class files on the passed input directory ({@link #iterateClassnames(String)}) and
  apply transformation to each one (
  {@link #transform(IClassTransformer, String, String, Iterator)}).
  <p>
  <strong>Limitation:</strong> do not search inside .jar files.
  </p>
  
  @param transformer The transformer that will apply transformations could be {@code null}.
  @param inputDir The root directory where the classes to transform will selected from could
  be {@code null} or empty. If it is {@code null} or empty nothing will be transformed.
  @param outputDir The output directory where the transformed classes will stored could be
  {@code null} or empty. If it is {@code null} or empty the {@code inputDir} will be
  used.
  
  @see #iterateClassnames(String)
  @see #transform(IClassTransformer, String, String, Iterator)