Array of Objects Manipulation

[DreamNaut]

Hello , I have a method that adds a new instance to an array of objects

public void addReservation(String gInput,int roInput,int bInput,double raInput, int nInput)
{
int roomsRented=0;
if(roomsRented<theRooms.length){
theRooms[roomsRented]=new Room(gInput,roInput,bInput,raInput,nInput);
roomsRented++;
}
}

I also have a constructor with the array of objects

public Hotel(String inputName){
name=inputName;
Room[] theRooms=new Room[NUM_ROOMS];
}

Now when I test this method

public class HotelTester{

public static void main(String[] args){

Hotel test1=new Hotel("Hilton");

test1.addReservation("John Doe",4,2,29.95,5);

}

it throws a null pointer exception error pointed to my addreservations method.


any advice on this? I am stumped. I suppose the addreservation method is incorrect but I don't see how it makes sense to me?!?

[eRaaaa]

because theRooms is a local variable and only visible in the constructor!

declare the variable outside:

private Room[] theRooms;

and initialize in the constructor theRooms=new Room[NUM_ROOMS]; (without Room[] at the beginning)

[DreamNaut]

ahh thank you, i did have the array declared as an instance variable but room[] theRooms=new(xxx) messed everything up :(

[DreamNaut]

I think I am declaring arrays illegally but the compiler is not catching it??

public int reportReservation(int rInput){

int i=0;
int x=theRooms[i].getNumber();
for (i = 0; i < theRooms.length; i++)
{
if (x==rInput){

System.out.println(theRooms[i].toString());
}
}
System.out.println("Reservation not found!");
return NOT_FOUND;


}

This code simply checks for a room number and if theres a match prints out an instance of the array, the match prints out, but then it throws a null pointer error highlighting System.out.println(theRooms[i].toString());

(the to string method is from the "room" class)

[berkeleybross]

some of the positions in "theRooms[]" are null - you either need to initialise (theRooms[i] = new Room()) them before you can use it, or you need to check if its null (if (theRooms[i] != null {System.out.println (theRooms[i].toString());}

[DreamNaut]

Thanks for the help so far, my methods are somewhat functional now

the only problem I have is when the add reservation method is used more then once, it overwrites the pre-existing element.

public void addReservation(String gInput,int roInput,int bInput,double raInput, int nInput)
{

int roomsRented=0;
if(roomsRented<theRooms.length){
theRooms[roomsRented]=new Room(gInput,roInput,bInput,raInput,nInput);
roomsRented++;
}

}

Now there is a code in my book:

if(roomsRented<theRooms.length)
{
for (int i=roomsRented; i>pos; i--){
theRooms[i] = theRooms[i-1];
}
theRooms[pos]= (new element);
roomsRented++;
}

which seems to work when setting the pos=0, but I don't understand how it works without having roomsRented defined? roomsRented is only defined as an instance variable. So shouldn't the compiler throw an error?

[berkeleybross]

Sorry, im being a little slow today, and cant really understand the question.

I think the "int roomsRented = 0" line is supposed to be a class variable (i.e. outside the addReservation method)