adding 2 arraylists to another arraylist

Question

I have 2 arraylist like this, but im not sure how i can combine them together. I have tried the Collections.copy() and addAll method but it wouldnt work, I want to know if there is any way I can combine them together into another arraylist? What I really want is to have the first arraylist storing the data from the second arraylist, so each of the Point would have a few lines inside it. Maybe you guys can give me some suggestions of how i can do this please, thanks.

 static ArrayList<Vertex> getPoints() {
      Scanner input = Reader(Vertex.airports);
      ArrayList<Vertex> result = new ArrayList<Vertex>();

      while(input.hasNext()){
          String point = input.nextLine();
          result.add(new Vertex(point));

      }
      input.close();
      return result;

  }

  static ArrayList<Edge> getlines(){
          Scanner input = Reader(Vertex.graph);
          ArrayList<Edge> result = new ArrayList<Edge>();

          while(input.hasNext()){
              String route = input.nextLine();
              result.add(new Edge(route));
          }
          input.close();
          return result;

      }

the data are from 2 text files, the file looks like this. They are just some of it to show what Im trying to do here. (index,name)

1 England
2 France

3 Holland

(index,start,cost,end)

1 1 2 2
2 1 3 1
3 1 6 3
4 1 7 3
5 2 1 2
6 2 3 1
7 2 4 1
8 2 5 2
9 2 6 2
10 3 1 1
11 3 2 1
12 3 4 1
13 3 8 1
14 3 10 2

thanks to Captain Ford this is completed!

Answer 1

Okay, my understanding is that the first list contains a list of airports, and the second list connects the airports in the first list.

If you want to store references to the lines with the associated points, you would need to create a wrapper around the points that contains another list.

class Airport {
    public Vertex point;
    public List<Edge> routes = new ArrayList<Edge>();

    public Airport(Vertex p){
        this.point = p;
    }
}

Then when you're loading your lists, you would do something like this:

static ArrayList<Airport> getAirports() {
    Scanner input = Reader(Vertex.airports);
    ArrayList<Vertex> result = new ArrayList<Vertex>();

    while(input.hasNext()){
        String point = input.nextLine();
        //  Note the small change on the next line
        result.add(new Airport(new Vertex(point)));

    }
    input.close();
    return result;
}

static ArrayList<Edge> getlines(){
    Scanner input = Reader(Vertex.graph);
    ArrayList<Edge> result = new ArrayList<Edge>();

    while(input.hasNext()){
        String route = input.nextLine();
        result.add(new Edge(route));
    }
    input.close();
    return result;

}

static void combineLists(List<Airport> airports, List<Edge> lines){
    for(Edge edge : lines){
        //  This is where we add the routes to both airports
        //  Since I don't know the structure of the edge class, I'm making a guess that you're using the integer indices that were described in the file to describe the endpoints. Note, however, that you will need to find a way to guarantee that they match the indices of the list of airports.
        airports.get(edge.p1).routes.add(edge);
        airports.get(edge.p2).routes.add(edge);
    }
}

Answer 2

I think I can improve on my other answer.

A more complete solution would look like this:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;

public class Airport {
    public final int id;
    public String name;
    public List<Route> outboundRoutes = new ArrayList<Route>();
    public List<Route> inboundRoutes = new ArrayList<Route>();

    public double minDistance;
    public Airport previous;

    public Airport(int id, String name){
        this.id = id;
        this.name = name;
    }

    public static class Route {
        public final int id;
        public double cost;
        public Airport departure;
        public Airport destination;

        public Route(int id, double cost, Airport departure, Airport destination){
            this.id = id;
            this.cost = cost;
            this.departure = departure;
            this.destination = destination;
        }
    }


    public static Map<Integer,Airport> readAirports(Scanner input){
        Map<Integer,Airport> airports = new HashMap<Integer,Airport>();
        while(input.hasNext()){
            //  Using a map rather than a list simplifies the process of loading 
            //  your routes, and eliminates problems that would crop up if some
            //  airports are listed out of order or removed.
            Airport port = new Airport(input.nextInt(), input.next());
            airports.put(port.id, port);
        }
        return airports;
    }


    //  Note that the list of airports must be passed when loading the routes, 
    //  but that nothing is returned -- the routes are loaded directly 
    //  into the airports.
    public static void readRoutes(Scanner input, Map<Integer,Airport> airports){

        while(input.hasNext()){
            int id = input.nextInt();
            int departureId = input.nextInt();
            int destinationId = input.nextInt();
            double cost = input.nextDouble();

            if(!(airports.containsKey(departureId) && 
                    airports.containsKey(destinationId))){
                //  You'll have to decide how to handle a situation when a route 
                //  refers to airports that don't exist
                throw new RuntimeException(
                        "Undefined airport referenced in route #" + id);
            }

            Route route = new Route(id, cost, airports.get(departureId), 
                    airports.get(destinationId));
            route.departure.outboundRoutes.add(route);
            route.destination.inboundRoutes.add(route);
        }
    }

    public static Map<Integer,Airport> loadAirports() throws FileNotFoundException {
        Scanner inAirports = new Scanner(new File("airports.txt"));
        Scanner inRoutes = new Scanner(new File("routes.txt"));
        Map<Integer,Airport> airports = readAirports(inAirports);
        readRoutes(inRoutes, airports);
        return airports;
    }

    public static void main(String[] args){
        try {
            Map<Integer,Airport> airports = loadAirports();
            for(Airport port : airports.values()){
                System.out.println(port.name + " has " + port.inboundRoutes.size() + " inbound routes and " + port.outboundRoutes.size() + " outbound routes ");
                for(Route r : port.inboundRoutes){
                    System.out.println("\tin from " + r.departure.name + " at a cost of $" + r.cost);
                }
                for(Route r : port.outboundRoutes){
                    System.out.println("\tout to " + r.destination.name + " at a cost of $" + r.cost);
                }
            }

        } catch (IOException e){
            e.printStackTrace();
        }
    }
}

If you wanted a simple, straight up answer, what you were wanting to do with ArrayLists can't be done without doing some kind of nesting.

Since you're working with data that has IDs, I would strongly recommend you use a HashMap anyway so you don't have to worry about your data not being in a perfect sequence. And since you have metadata (airport names), creating these classes is a good way to model the data.

Edit: Code has now been altered to all fit in one file. With the sample files you provided called "airports.txt" and "routes.txt" respectively, it should work just fine. When you run it, you should get the following output:

England(LHR) has 4 inbound routes and 4 outbound routes 
    in from France(CDG) at a cost of $2.0
    in from Holland(AMS) at a cost of $1.0
    in from Portugal(LIS) at a cost of $3.0
    in from Iceland(KEF) at a cost of $3.0
    out to France(CDG) at a cost of $2.0
    out to Holland(AMS) at a cost of $1.0
    out to Portugal(LIS) at a cost of $3.0
    out to Iceland(KEF) at a cost of $3.0
France(CDG) has 5 inbound routes and 5 outbound routes 
    in from England(LHR) at a cost of $2.0
    in from Holland(AMS) at a cost of $1.0
    in from Germany(FRA) at a cost of $1.0
    in from Italy(LIN) at a cost of $2.0
    in from Portugal(LIS) at a cost of $2.0
    out to England(LHR) at a cost of $2.0
    out to Holland(AMS) at a cost of $1.0
    out to Germany(FRA) at a cost of $1.0
    out to Italy(LIN) at a cost of $2.0
    out to Portugal(LIS) at a cost of $2.0
Holland(AMS) has 5 inbound routes and 5 outbound routes 
    in from England(LHR) at a cost of $1.0
    in from France(CDG) at a cost of $1.0
    in from Germany(FRA) at a cost of $1.0
    in from Denmark(CPH) at a cost of $1.0
    in from Finland(HEL) at a cost of $2.0
    out to England(LHR) at a cost of $1.0
    out to France(CDG) at a cost of $1.0
    out to Germany(FRA) at a cost of $1.0
    out to Denmark(CPH) at a cost of $1.0
    out to Finland(HEL) at a cost of $2.0
Germany(FRA) has 4 inbound routes and 4 outbound routes 
    in from France(CDG) at a cost of $1.0
    in from Holland(AMS) at a cost of $1.0
    in from Italy(LIN) at a cost of $1.0
    in from Sweden(ARN) at a cost of $2.0
    out to France(CDG) at a cost of $1.0
    out to Holland(AMS) at a cost of $1.0
    out to Italy(LIN) at a cost of $1.0
    out to Sweden(ARN) at a cost of $2.0
Italy(LIN) has 3 inbound routes and 3 outbound routes 
    in from France(CDG) at a cost of $2.0
    in from Germany(FRA) at a cost of $1.0
    in from Portugal(LIS) at a cost of $3.0
    out to Portugal(LIS) at a cost of $3.0
    out to France(CDG) at a cost of $2.0
    out to Germany(FRA) at a cost of $1.0
Portugal(LIS) has 3 inbound routes and 3 outbound routes 
    in from England(LHR) at a cost of $3.0
    in from France(CDG) at a cost of $2.0
    in from Italy(LIN) at a cost of $3.0
    out to England(LHR) at a cost of $3.0
    out to France(CDG) at a cost of $2.0
    out to Italy(LIN) at a cost of $3.0
Iceland(KEF) has 1 inbound routes and 1 outbound routes 
    in from England(LHR) at a cost of $3.0
    out to England(LHR) at a cost of $3.0
Denmark(CPH) has 2 inbound routes and 2 outbound routes 
    in from Holland(AMS) at a cost of $1.0
    in from Norway(OSL) at a cost of $1.0
    out to Holland(AMS) at a cost of $1.0
    out to Norway(OSL) at a cost of $1.0
Norway(OSL) has 2 inbound routes and 2 outbound routes 
    in from Denmark(CPH) at a cost of $1.0
    in from Sweden(ARN) at a cost of $1.0
    out to Denmark(CPH) at a cost of $1.0
    out to Sweden(ARN) at a cost of $1.0
Finland(HEL) has 2 inbound routes and 2 outbound routes 
    in from Holland(AMS) at a cost of $2.0
    in from Sweden(ARN) at a cost of $1.0
    out to Sweden(ARN) at a cost of $1.0
    out to Holland(AMS) at a cost of $2.0
Sweden(ARN) has 3 inbound routes and 3 outbound routes 
    in from Germany(FRA) at a cost of $2.0
    in from Norway(OSL) at a cost of $1.0
    in from Finland(HEL) at a cost of $1.0
    out to Germany(FRA) at a cost of $2.0
    out to Norway(OSL) at a cost of $1.0
    out to Finland(HEL) at a cost of $1.0