public void addStep(final IStep step){
  if (step == null)   throw new IllegalArgumentException();
  if (step == this)   throw new IllegalArgumentException();
  steps.add(step);
}

public void addStep ( final IStep step ) { if ( step == null ) throw new IllegalArgumentException ( ) ; if ( step == this ) throw new IllegalArgumentException ( ) ; steps . add ( step ) ; }
add another step in the program .
