......
// first, count filled position   
     int count = 0;

     List<IOrder> AllPositions  = engine.getOrders(instrument);
     for (IOrder order: AllPositions) {
            if (order.getState().equals(IOrder.State.FILLED)){
                   count = count  + 1;
       }
     }

// then if open positions > 10, close all position
     if ( count >= 10 ){
           // in real life after executing order.close(), AllPositions might point to invalid data
           // so this code below is not recomended, but hope you got the idea 
           for (IOrder order: AllPositions) {
                 if (order.getState().equals(IOrder.State.FILLED)){
                   order.close();
                         // should wait some time here 
           }
           }
     }
.......