question: public static ArrayList < Hop > deepCopyHopsDag ( ArrayList < Hop > hops ) throws HopsException { ArrayList < Hop > ret = new ArrayList < Hop > ( ) ; try { HashMap < Long , Hop > memo = new HashMap < Long , Hop > ( ) ; for ( Hop hopRoot : hops ) ret . add ( rDeepCopyHopsDag ( hopRoot , memo ) ) ; } catch ( Exception ex ) { throw new HopsException ( ex ) ; } return ret ; }
target:  Deep copy of hops dags for parallel recompilation.