private int registerSourceFile(String file){
  if (sourceFiles.contains(file))   return -1;
  sourceFiles.add(file);
  this.size++;
  return sourceFiles.size() - 1;
}

private int registerSourceFile ( String file ) { if ( sourceFiles . contains ( file ) ) return - 1 ; sourceFiles . add ( file ) ; this . size ++ ; return sourceFiles . size ( ) - 1 ; }
register a new source file . this method is used to implement file inclusion . each included file gets a unique identifier ( which is the index in the array of source files ) .
