CODEWITHSUNDEEP
javaarraylist
user1176922
user1176922

Reputation: 93

Java: Accessing an ArrayList inside an ArrayList?

In FleetTUI.java I have a list of Fleets (Each fleet will hold its own list of Trucks).

private static ArrayList<Fleet> fleetCollection;

In Fleet.java, I have a list of Truck objects.

ArrayList<Truck> fleetList;

which gets initialized in it's constructor.

    public Fleet(String businessName){
    this.businessName = businessName;
    this.fleetList = new ArrayList<Truck>();
}

So every time I make a new fleet, I am also making a list of Trucks along with it.

In FleetTUI.java, I have a method that adds a truck to a Fleet, made prior:

    public static void addTruck(){
    printFleets();
    System.out.println("Please enter the fleet number where this truck will be added:");
    inputText = scan.nextLine();
    int inputFleetId = Integer.parseInt(inputText);
    System.out.println("Please enter the truck's horn sound:");
    inputText = scan.nextLine();
    String inputHorn = inputText;
    System.out.println("Please enter the truck's fuel capactity:");
    inputText = scan.nextLine();
    int inputFuelCapacity = Integer.parseInt(inputText);
    System.out.println("Please enter the amount of gas remaining in the tank:");
    double inputGasRemaining = Double.parseDouble(scan.nextLine());
    **Fleet.fleetList**.add(inputFleetId, new Truck(inputHorn, inputFuelCapacity, inputGasRemaining));
    System.out.println("--- A truck that goes " + inputHorn + " with " + inputGasRemaining + " gallon(s) in a " + inputFuelCapacity + " gallon tank has been added to " + **fleetCollection.getBusinessName()** + "'s fleet ---" );
    System.out.println("");
}

I have bolded where I am getting errors. The errors are:

Cannot make a static reference to the non-static field Fleet.fleetList

Cannot make a static reference to the non-static method getBusinessName() from the type Fleet

I don't know any other way to access the list of trucks from inside the fleet I created with the method:

    public static void createFleet(){
    System.out.println("");
    System.out.println("Please enter the name of the fleet.");
    inputText = scan.nextLine();
    
    fleetCollection.add(new Fleet(inputText));
    printFleets();
    System.out.println("");
    System.out.println("--- Fleet: " + inputText + " added ---");
    System.out.println("");
    
}

So I guess really, my question is: How do I correctly add a new Truck into the list of Trucks, which is inside the Fleet I just made using createFleet(), which is housed in it's own collection of fleets?

Update: Thanks :) you guys really helped me! once again!

Upvotes: 1

Views: 2865

Answers (2)

npinti
npinti

Reputation: 52185

Your problem is that you are creating static methods within which you are then trying to access a non-static variable, in this case this being fleetlist. This will cause the error you are showing.

Since you are using a constructor and everything, you do not need to call the method static. Calling it static will allow the method to be called without the object needing to be constructed, which from what I am seeing is not something you are after.

So in short, make your methods non-static by removing the static keyword from the method declaration and access your methods such as addTruck() and createFleet() through the use of the initialized Fleet object.

On the other hand, you can declare your fleetlist to be static, like so: 

private static ArrayList<Truck> fleetList;

EDIT: Seeing your comment, this is how you can do it:

In Java, it is considered good practice to encapsulate your object variables so that you can better control the access to such variable, so you can do something like so in your Fleet Class:

private List<Truck> fleetList;

public Fleet(String businessName){
    this.businessName = businessName;
    this.fleetList = new ArrayList<Truck>();
}

public List<Truck> getFleetList()
{
    return this.fleetList;
}

In your FleetUI Class you can do something like so:

private ArrayList<Fleet> fleetCollection;    
...   
for (Fleet fleet : this.fleetCollection)
{
    for (Truck truck : fleet.getFleetList())
    {
         //Do something with your truck here
    }
}

EDIT 2: To add a truck to your array, you can do it in 2 ways. Let us assume that the object fleet is the Fleet to which you want to add your truck. In your FleetUI class you can do like so:

fleet.getFleetList().add(new Truck(...))

The other (and in my opinion, better way) is to have an addTruck method in your fleet object like so:

public void addTruck(Truck truck)
{
    this.fleetList.add(truck);
}

Upvotes: 2

aviad
aviad

Reputation: 8278

  1. You are calling

    Fleet.fleetList.add()

    method from the static method addTruck.

  2. It is bad practice to reference a member like this:

    Fleet.fleetList.add

    you should introduce some accessor method to add a truck to a flletList in your Fleet class

Upvotes: 1

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