CODEWITHSUNDEEP
javaarrayslist
Joaocdn
Joaocdn

Reputation: 247

How to dynamically create Lists in java?

I'm programming in java for a class project. In my project I have airplanes, airports and passengers.

The passenger destination airport is randomly created, but then I have to add it to a List with passengers for that destination.

As long as the airports are read from a file thus they can vary, how can I create Lists according to these airports?

What I want to do is something like:

List<Passenger> passengersToJFK = new ArrayList<Passenger>();
.
.
.

if(passenger.destination == "JFK"){
   passengersToJFK.add(passenger);
}

The problem is that as I've said, the number and name of airports can vary, so how can I do a general expression that creates Lists according to the Airports File and then adds passengers to those Lists according to the passenger destination airport?

I can get the number of Airports read from the file and create the same number of Lists, but then how do I give different names to this Lists?

Thanks in advance

Upvotes: 2

Views: 15723

Answers (5)

Fritz
Fritz

Reputation: 10055

You can keep a registry of the associations between a destination or airport and a list of passengers with a Map, in a particular class that centers this passengers management.

Map<String,List<Passenger>> flights = new HashMap<String,List<Passenger>>();

Then, whenever you want to add a new destination you put a new empty list and

public void addDestination(String newDestination) {
    flights.put(newDestination, new ArrayList<Passenger>());
}

When you want to add a passenger, you obtain the passenger list based on the destination represented by a String.

public void addPassengerToDestination(String destination, Passenger passenger) {
    if(flights.containsKey(destination))
        flights.get(destination).add(passenger);        
}

I suggest you dig a little deeper into some particular multi-purpose Java classes, such as Lists, Maps and Sets.

Upvotes: 9

Bill K
Bill K

Reputation: 62789

The best way to do it is to create objects for all three.

You might have an Airport object that looks like this:

    class Airport{
        String name;
        List Airplane airplanes;
    }

then you would have an airplane that looked like this:

    class Airplane{
        String name; // ?? or bodyType?  or whatever else you need
        List Passenger passengers;
    }

In this way you compose your objects from each other in a way that ends up being much easier to understand and deal with.

Note that I'm leaving off methods, like Airport probably has a method like "addAirplane" to add another airplane, and the airplane object has an addPassenger method...

Upvotes: 0

Tom Teman
Tom Teman

Reputation: 2013

You shouldn't focus on giving the actual variables of list objects unique names, but instead, create a map from String (destination id) to List (passengers heading to that destination), and add lists on the fly to that map, linking each new list to its relevant destination. Update the lists in that map as needed.

Upvotes: 0

cowls
cowls

Reputation: 24354

I would probably create a Map of airports with airport name as the key and a List of passengers as the value.

e.g.

Map<String, List<String>> airports = new HashMap<String, List<String>>();

airports.put("JFK", passengersToJFK);

Upvotes: 2

duffymo
duffymo

Reputation: 308998

You sound like you're thinking too much in terms of primitives, Strings, and collections and not enough in terms of objects.

Java's an object-oriented language; start thinking about Objects and encapsulation.

You've got a good start with your Passenger class. Keep going with Airport.

Do you add Passengers to Airport? Nope, I think they belong to a Flight.

Do a little thinking about your problem before you write more code.

Upvotes: 0

Related Questions