java - NullPointerException in booking app -

i'm getting nullpointerexception at:

if(bookinglist.size() == 0) 

,

bookinglist.add(vehiclebooking)  

and

bookinglist.add(rvbooking)  

and not sure causing it. appreciated.

stack trace

bookingsystem.ferrybookingsystem @ localhost:59034      thread [main] (suspended (exception nullpointerexception))           ferrybookingsystem.bookingidexists(string) line: 35          ferrybookingsystem.addvehiclebooking() line: 49          ferrybookingsystem.main(string[]) line: 114  c:\program files\java\jre7\bin\javaw.exe (14/05/2013 10:52:02 pm) 

bookingexception

    package bookingsystem;      import java.util.arraylist;     import java.util.scanner;     import java.io.*;       class bookingexception extends exception{        string message;        string ids;         public bookingexception(string message){           this.message = message;        }        public bookingexception(string message, string ids){           this.message = message;           this.ids = ids;        }        public string getids(){           return ids;        }        public string getmessage(){           return message;        }     } 

ferrybookingsystem

    public class ferrybookingsystem {     private static arraylist<vehiclebooking> bookinglist;     private static scanner userinput = new scanner (system.in);      public ferrybookingsystem(){         bookinglist = new arraylist<vehiclebooking>();     }      public static int bookingidexists(string ids){        if (bookinglist.size() == 0)              return -1;           (int = 0; < bookinglist.size(); i++){              if(bookinglist.get(i).getbookingid().equals(ids))                 return i;           }           return -1;        }        public static boolean addvehiclebooking(){         system.out.print("please enter booking id: ");         string booking_id = userinput.nextline();          if(bookingidexists(booking_id) != 1)       {                  system.out.println("\nerror - sale id \"" + booking_id +                 "\" exists in system!");          return false;       }          system.out.print("please enter registration number vehicle: ");         string registration_number = userinput.nextline();         system.out.print("please enter vehicle " +                 "description: ");         string vehicle_description = userinput.nextline();         system.out.print("please enter number of people travelling in vehicle: ");         int travelling_number = userinput.nextint();         userinput.nextline();         vehiclebooking vehiclebooking = new vehiclebooking(booking_id, registration_number, vehicle_description, travelling_number);         bookinglist.add(vehiclebooking);         system.out.println("new vehicle booking added " + booking_id);         return true;     }      public static boolean addrecreationalvehiclebooking(){        system.out.print("please enter booking id: ");        string booking_id = userinput.nextline();         system.out.print("please enter registration number vehicle: ");        string registration_number = userinput.nextline();        system.out.print("please enter vehicl description: ");        string vehicle_description = userinput.nextline();        system.out.print("please enter number of people travelling in vehicle: ");        int travelling_number = userinput.nextint();        userinput.nextline();        rvbooking rvbooking = new rvbooking(booking_id, registration_number, vehicle_description, travelling_number);        bookinglist.add(rvbooking);        system.out.println("new rvbooking added " + booking_id);        return true;     }      public static void displaybookingsummary(){        if (bookinglist.size() != 0){           system.out.println("\nsummary of past vehicle booking stored on system.");           (int i=0 ; i<bookinglist.size() ; i++){              bookinglist.get(i).printbookingsummary();              system.out.println("");           }        }     }      public static void main (string [] args) throws ioexception{         char user;         do{         system.out.println("**** ferry ticketing system ****");         system.out.println("   -   add vehicle booking");         system.out.println(" b   -   add recreational vehicle booking");         system.out.println(" c   -   display booking summary");         system.out.println(" d   -   update insurance status");         system.out.println(" e   -   record recreational vehicle weight");         system.out.println(" f   -   compile vehicle manifest");         system.out.println(" x   -   exit");         system.out.print("enter selection: ");         string choice = userinput.nextline().touppercase();         user = choice.length() > 0 ? choice.charat(0) : '\n';         if (choice.trim().tostring().length()!=0){         switch (user){             case 'a':                 addvehiclebooking();                 break;             case 'b':                addrecreationalvehiclebooking();                 break;             case 'c':                displaybookingsummary();                 break;             case 'd':                 break;             case 'e':                 break;             case 'f':                 break;             case 'x':                 break;             default:                 break;                 }         }         }while(user!='x');     } } 

move initialization of bookinglist regular constructor static initialization block:

static {     bookinglist = new arraylist<vehiclebooking>(); } 

or initialize @ point of declaration:

private static arraylist<vehiclebooking> bookinglist = new arraylist<vehiclebooking>(); 

otherwise, bookinglist remain null until first call of ferrybookingsystem's constructor made.