How do you create an integer ArrayList? [duplicate]

Question

I am trying to create an array of Arraylists in Java. I have declared it in the following way:

ArrayList[][][] arrayQ = new ArrayList[90][13][18];

for (int i = 0; i < 90; i++) {
  for (int j = 0; j < 13; j++) {
    for (int k = 0; k < 18; k++) {
      arrayQ[i][j][k] = new ArrayList<int>();
    }  
  } 
}

However, adding the <int> inside the while loop throws an error (the IDE I'm using unfortunately doesn't give me a very good error message).

What's the proper way to create an integer ArrayList?

now what if I wanted to use the integer value and pass it to a function that takes an int? because if I try to pass it something like function(arrayQ[i][j][0].get(k), 77) it is passing this as an Integer object. how would I case it to a primitive int? — Tomek
– Tomek, Commented Nov 2, 2010 at 5:37

joschi · Accepted Answer · 2010-11-02 05:25:30Z

10

Java Collections can only hold objects. int is a primitive data type and cannot be held in an ArrayList for example. You need to use Integer instead.

answered Nov 2, 2010 at 5:25

joschi

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Comments

rjmoggach · Accepted Answer · 2011-08-25 05:51:33Z

4

Here's a complete example:

ArrayList<Integer>[] foo = new ArrayList[3];

foo[0] = new ArrayList<Integer>();
foo[1] = new ArrayList<Integer>();
foo[2] = new ArrayList<Integer>();

foo[0].add(123);
foo[0].add(23);
foo[1].add(163);
foo[1].add(23789);
foo[2].add(3);
foo[2].add(2);

for (ArrayList<Integer> mylist: foo) {
  for (int bar : mylist) {
    println(bar);
  }
}

answered Aug 25, 2011 at 5:51

rjmoggach

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Comments

Andy Dvorak · Accepted Answer · 2010-11-02 05:28:08Z

3

joschi and Cristian are correct. Change new ArrayList<int>() to new ArrayList<Integer>() and you should be fine.

If at all possible, I would recommend using Eclipse as your IDE. It provides (usually) very specific, detailed, and generally helpful error messages to help you debug your code.

answered Nov 2, 2010 at 5:28

Andy Dvorak

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Comments

EboMike · Accepted Answer · 2010-11-02 05:28:32Z

2

The problem is that an ArrayList requires Objects - you cannot use primitive types.

You'll need to write arrayQ[i][j][k] = new ArrayList<Integer>();.

answered Nov 2, 2010 at 5:28

EboMike

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Comments

Andy White · Accepted Answer · 2010-11-02 05:25:43Z

1

It looks like you're mixing the non-generic and generic ArrayLists. Your 3D array of ArrayList uses the non-generic, but you are trying to assign a generic ArrayList<int>. Try switching one of these to match the other.

answered Nov 2, 2010 at 5:25

Andy White

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