private List<Queen> createQueenList(NQueens nQueens) { int n = nQueens.getN(); List<Queen> queenList = new ArrayList<Queen>(n); long id = 0; for (Column column : nQueens.getColumnList()) { Queen queen = new Queen(); queen.setId(id); id++; queen.setColumn(column); // Notice that we leave the PlanningVariable properties on null queenList.add(queen); } return queenList; }