Java ArrayList of Integer[], how to access elements

Question

I am using an ArrayList of to create lists. For example:

Index 0: 1 3
Index 1: 4 5
Index 2: 1 3 7

How can I access the second element of the first index of the ArrayList? Couldn't find the answer on Google, so I asked here.

I googled "ArrayList of integers" and the first result was http://stackoverflow.com/questions/14421943/java-arraylist-for-integers — Hanlet Escaño, Jan 08 '15 at 16:22
Show us some code, because a `ArrayList` isn't an array of `Integer`(s). — Elliott Frisch, Jan 08 '15 at 16:23
I mean if its a true Arraylist. You could use `myList.get(0)` which would return the first index, but past that I don't know :P — Adam, Jan 08 '15 at 16:23
I found the correct answer on @Fev, I don't use a 2d Array because it's harder to add elements dinamically. ArrayList of integer[] it's much easier. — Marian Pavel, Jan 08 '15 at 16:27
@PavelMarian Sounds like you should be using a `List> al = new ArrayList<>();` why use one dynamic collection and a fixed width object? — Elliott Frisch, Jan 08 '15 at 16:29
@HanletEscaño That looks like an accident. This is about an "ArrayList of arrays of integers", not "ArrayList of integers". But the second phrase happened to work because someone put the wrong title on their question. My point is: don't assume that everyone should just be able to find things with Google. It's not always easy to guess what search terms to put in. — ajb, Jan 08 '15 at 16:32

score 4 · Accepted Answer · edited Jan 08 '15 at 16:36

4

yourList.get(0)[1]; // that's it !!

If you want to iterate over it :

for (Integer[] outer : yourList) {
  for(Integer inner : outer) {
    System.out.println(inner);
  }
}

edited Jan 08 '15 at 16:36

David Conrad

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answered Jan 08 '15 at 16:23

Fevly Pallar

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If it was so simple why I couldn't find it over the internet, thanks a lot.Gonna try it ! Mark answer after time pass. – Marian Pavel Jan 08 '15 at 16:26

score 2 · Answer 2 · answered Jan 08 '15 at 16:25

By your question, I am guessing you have something like this?

List<Integer[]> list = new ArrayList<Integer[]>();
Integer[] a1 = {1,3};
Integer[] a2 = {4,5};
Integer[] a3 = {1,3,7};

list.add(a1);
list.add(a2);
list.add(a3);

Then all you need to do is simply call:

Integer result = list.get(0)[1];

The get(0) pulls the first Integer[] out of the list, then to get the second element, you use [1]

score 0 · Answer 3 · answered Jan 11 '15 at 10:53

where do you see the exception? have you tried this?

    List<Integer[]> list = new ArrayList<Integer[]>(3);
    Integer[] a1 = {1,3};
    Integer[] a2 = {4,5};
    Integer[] a3 = {1,3,7};

    list.add(a1);
    list.add(a2);
    list.add(a3);

    Integer result = list.get(0)[1];

There aren't any exception. The arraylist have three elementes because you have three elemente (a1,a2,a3),

score -1 · Answer 4 · edited Jan 09 '15 at 13:15

-1

You have List<Integer[]> l = new ArrayList<Integer[]>(3);

if you want the second element of the first index:

l.get(0)[1].

edited Jan 09 '15 at 13:15

Ascalonian

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answered Jan 08 '15 at 16:35

nole

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Your declaration of the `List` won't even compile. Did you mean to put something else? – Ascalonian Jan 08 '15 at 17:30
I forgot >, List l = new ArrayList(3); and afer that, you have to fill the list. – nole Jan 09 '15 at 08:03
Your code will also throw an `IndexOutOfBoundsException` – Ascalonian Jan 09 '15 at 13:17
if you want the second element, you need a for. My answer was a example. for (int i=0;i<3; i++) – nole Jan 11 '15 at 10:54

Java ArrayList of Integer[], how to access elements

4 Answers4