An array of ArrayLists?

Question

So, simple question that seems to be baffling me. I have a series of ArrayList because they need to be expandable. Now, I would like to be able to pull the nth object from each one with a simple for loop.

public ArrayList<String> name = new ArrayList<String>();
public ArrayList<Integer> stamina = new ArrayList<Integer>();
public ArrayList<Integer> heart = new ArrayList<Integer>();
public ArrayList<Integer> intel = new ArrayList<Integer>();
public ArrayList<Integer> speed = new ArrayList<Integer>();

I'll be adding/pulling information from these later in my code, so I would like it to be easily accessible via a single 2D array. With something like,

racerInfo[][] = { name, stamina, heart, intel, speed };

Then if I want information for, say, racer number 7

for ( int i=0; i<=racerInfo.length - 1; i++ ) {
    System.out.println(racerInfo[i][7]);
}

How would I go about setting up the racerInfo field? I can't seem to figure out the right setup. If you have any better suggestions for the rest I am completely open as I am still very new to this and just attempting to cobble something together that works.

Sorry, not answering the original question, but what you really want is a wrapper object e.g. RacerInfo instead of an array of lists. Also - a bit nit-picky - Try to create collections against their interfaces, not there implementations (List list = new ArrayList()) — Jan Groth
– Jan Groth, Commented Sep 10, 2014 at 2:07
Sasvathan, I have no idea what a pojo class is. I've never heard of those before. — MiuKujo
– MiuKujo, Commented Sep 10, 2014 at 2:16

kba · Accepted Answer · 2014-09-10 02:36:45Z

8

Your approach is a bit primitive, and you wouldn't have this problem if you had a better architecture.

Instead of having a bunch of lists of racer properties, you should create a racer class with the properties.

class Racer {
    private String name;
    private int stamina;
    ...
    public Racer(String name) {
       this.stamina = Math.random(...);
       ...
    }

    public function getStamina() {
       return this.stamina;
    }
}

Then you instantiate all your racers

Racer racer1 = new Racer("Alice");

and put them in a single list (or possibly a map) of racers:

List<Racer> racers = new ArrayList<Racer>();
racers.add(racer1);

or you could add them directly without first assigning them to a variable

racers.add(new Racer("Bob"));

edited Sep 10, 2014 at 2:36

answered Sep 10, 2014 at 2:09

kba

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6 Comments

x4nd3r Over a year ago

A much better solution.

takendarkk Over a year ago

I think you should also add to your answer how to get Racer objects into the list eg racers.add(new Racer(someString, someInt, ...))

MiuKujo Over a year ago

I don't think I'm understanding how this works. So, later on I'm going to use Math.random() to generate the stats for a racer. I know how I would add it to the list you've indicated, but how would I then pull the stats for display/implementation later? Like. I'm not sure what is storing the info or where it is being stored.

kba Over a year ago

@MiuKujo I've added an example of how you do it. This is a very basic usage of plain Java objects. It's very fundamental and important that you understand how objects like these work, otherwise you won't get very far with Java.

kba Over a year ago

@MiuKujo Creating these is no more manual than creating whatever you were doing before, I assure you. Why do you think creating these is more difficult?

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Avinash Kumar Pandey · Accepted Answer · 2014-09-10 02:08:11Z

0

make racerInfo an arrayList of arrayLists, something like this

ArrayList<ArrayList> racerInfo = new ArrayList<ArrayList>(Arrays.asList(new ArrayList[]{name, stamina, heart, intel, speed}));

answered Sep 10, 2014 at 2:08

Avinash Kumar Pandey

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