How to make different instances of a class?

Answer 1

To start off, a Hotel has more than one Room. Depending on what you've learnt as far, you should be using an array to hold all Room instances

Room[] rooms;

Hotel() {
    rooms = new Room[4];
}

or an ArrayList

List<Room> rooms;

Hotel() {
    rooms = new ArrayList<Room>();
}

See also:

• Arrays tutorial
• Collections tutorial

---

Update as per your comment: just check every room if it has a guest until you find a room without a guest (like as in real world!). Pseudo:

if there is no guest in room1, then use room1;
else if there is no guest in room2, then use room2;
else if there is no guest in room3, then use room3;
else if there is no guest in room4, then use room4;
else say "sorry, no rooms left!";

This is by the way easier to do in a simple loop when you use an array.

for each room, check if there is no guest in room, then use room;
if there is no room, then say "sorry, no rooms left!";

Oh, don't forget to make the guest null when s/he leaves the room. This will make the room eligible for reuse.

See also:

• if-then-else statements
• for statement

Answer 2

class Hotel {

Room room1, room2, room3, room4;

    Hotel() {
        room1 = new Room();
        room2 = new Room();
        room3 = new Room();
        room4 = new Room();
    }

}

If you haven't learned an Array yet.

But an Array (or ArrayList) is a better way to do this.

Answer 3

the next person that checks in will check in room 2

This can't be done right now. Your hotel only has one room! It should have more, 3 for example:

class Hotel {

  Kamer kamer1;
  Kamer kamer2;
  Kamer kamer3;

  Hotel (){
    kamer1 = new Kamer();
    kamer2 = new Kamer();
    kamer3 = new Kamer();
  }
}

Or better use arraylist

class Hotel {
  ArrayList<Kamer> kamers;

  Hotel (){
    kamers = new ArrayList<Kamer>();//make room-list
    kamers.add( new Kamer() );//add one room
    kamers.add( new Kamer() );//add one room
    kamers.add( new Kamer() );//add one room
    //more?
  }
}

If you need a hotel with 3 rooms, just call: new Hotel();.

static void checkIn() {
   Kamer k1 = new Kamer(g1.naam);

Why are you making a new room when someone wants to check in? You can't just build a new room if you need one, right? If you remove the static you can use the fields kamer1, kamer2 (or kamers if you used the ArrayList).

 void checkIn()
 {
   if (kamer1.guest==null)
      //kamer1 is available!
   //
   //

Answer 4

Hi sjaak,

a comment on the static (also noticed by Ishtar).

If you make checkIn static on the Hotel class (and not instance) you are saying that checkIn is the same over all hotels, and not just your hotel. That suggests that if you have 5 hotels, each with its own rooms, all the rooms are alike. So you could checkIn in hotel 1 and get a room from hotel 2. That's really not what you want to do.

public class Hotel   {
  // stuff

  // Check a guest into this hotel
  public Room instanceCheckIn(Guest guest) {
    //stuff
  }

  // Check a guest into one of our hotels. It doesn't matter to which 
  // particular hotel this room belongs :)
  public static Room staticCheckIn(Guest guest) {
    //stuff
  }
}

Usage:

Hotel instanceHotel = new Hotel();
// check a guest into a room of this hotel (instanceHotel)
instanceHotel.instanceCheckIn(someGuest);

// Check a guest into one of the rooms of our hotels
Hotel.staticCheckIn(someGuest);

// Error: cannot call a non-static method on a class
Hotel.instanceCheckIn(someGuest); 

// Technically OK, but incredibly bad taste. You suggest something
// is happening with this hotel (called instanceHotel) but in stead
// your actually working on all hotels together (shared data).
instanceHotel.staticCheckIn(someGuest);

In general it's a very good habit to not use static unless you really need it. It suggests something is broken in your domain model. That does not mean you should not use it, but realize that it has a particular odor. (public static void main(String[] args) is of course a special case).