Defining a 2D ArrayList with multiple ArrayLists inside

Question

ArrayList<ArrayList<String>, ArrayList<String>, ArrayList<String>> newlist = new ArrayList<ArrayList<String>, ArrayList<String>, ArrayList<String>>();

Above is my horrible ArrayList definition. I am trying to define an ArrayList containing multiple ArrayList inside although it gives me an Incorrect number of arguments error.

facilities = {
 [parking]
 [bike]
 [disability]
}

I am trying to make an ArrayList to hold this data above The main ArrayList (Facilities) will contain the inner ArrayLists. What is the correct way to define an ArrayList of ArrayLists?

You have multiple way to do it. Why would you need this? Why not use arrays? — Yassin Hajaj, Apr 18 '18 at 21:34
@YassinHajaj well, then you have lost the advantage of a `List` :D — Neuron, Apr 18 '18 at 22:38

rgettman · Answer 1 · 2018-04-18T23:08:51.783

First, ArrayList has only one type parameter, the type of all objects it contains, not each individual object. Second, an ArrayList is not the correct choice for storing related data that should be in its own object.

Fixing just the first problem would result in you defining your ArrayList as:

ArrayList<ArrayList<String>>

Additionally, usually you would program to the interface and define the variable as

List<List<String>>

You are free to use ArrayList or any other list as concrete implementations, of course, e.g.:

List<List<String>> newList = new ArrayList<>();

The second thing to fix would be to create a Facility class to encapsulate parking, bike, and disability. Then your list to hold Facility objects becomes simply:

List<Facility> newList = new ArrayList<>();

score 0 · Answer 2 · edited Apr 18 '18 at 21:36

0

You use:

ArrayList<ArrayList<String>> array = new ArrayList<>();
array.add(//Your arrayList here);

You add ArrayLists to it just like you would Strings to a regular ArrayList of Strings.

edited Apr 18 '18 at 21:36

Neuron

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answered Apr 18 '18 at 21:32

GBlodgett

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score 0 · Answer 3 · answered Apr 18 '18 at 21:32

0

ArrayList<ArrayList<String>> listOfLists = new ArrayList<>();

answered Apr 18 '18 at 21:32

Owen

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Explanation please? – Yassin Hajaj Apr 18 '18 at 21:33
It declares ArrayList of ArrayLists of Strings :) – Kermi Apr 18 '18 at 21:35
1

@Kermi it is a really poor answer if it doesn't explain the code. Don't just give people a solution, tell them **why** this is the solution. – Neuron Apr 18 '18 at 21:37

Defining a 2D ArrayList with multiple ArrayLists inside

3 Answers3