The queuingOrders array list can only be added by checkInOrder method without any other method removing orders from it. The onDelivery array list can only be removed by checkOutOrder method without any other method adding orders to it, thus the onDelivery list is always empty, and the checkOutOrders cannot work at any time. There should be some statements add order to the onDelivery and remove order from queuing orders.
Created attachment 8 [details] The source code
Hi the bug is solved