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

ArrayList[][][] arrayQ;
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. Unfortunately, I am programming with the Processing IDE and it doesn't give me a very good error that I can analyse to fix syntax problems.

Does this syntax seem correct?

Thanks,

Tomek

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new ArrayList<Integer>(); – Cristian Nov 2 '10 at 5:25
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 Nov 2 '10 at 5:37
Just write new Integer(77) instead of the int literal. – joschi Nov 2 '10 at 7:18
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5 Answers

up vote 0 down vote

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);
  }
}
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up vote 0 down vote

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>();.

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up vote 1 down vote

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.

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up vote 1 down vote

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.

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up vote 3 down vote

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.

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