public static ArrayList<Vehicle> al=new ArrayList<Vehicle>();
    java.util.Iterator<Vehicle> itr= al.iterator();

    @SuppressWarnings("unchecked")
    public boolean addVehicleToSlot(Vehicle vehicle) {
        if((vehicle.slotNo<=0||vehicle.slotNo>40)&&(vehicle.getVehicleType()!="Car"
                ||vehicle.getVehicleType()!="Truck"||vehicle.getVehicleType()!="Two Wheeler")){
            new InvalidSlotException("Slot alraedy allotted");
            return false;
        }
        int iter=0;
        int len=al.size();
        if(len==0){
            al.add(vehicle);
            return true;
        }
        while(iter< len){
            Vehicle veh=(Vehicle)itr.next();
            if(veh.getSlotNo()==vehicle.getSlotNo()){
                new SlotNotFoundException("No slot allotted");
                return false;
            }
            else{
                al.add(vehicle);
                for(Vehicle vehi:al){
                    System.out.println(al);
                }
                return true;
            }
        }
        return false;
    }

Vehicle v1=new Vehicle(o1,"ts75","Truck",37,48);
    ParkingManagement p1=new ParkingManagement();
    System.out.println(p1.addVehicleToSlot(v1));