Return an array by converting from an ArrayList in Java

Question

I need to create a method to return an int array by casting from the ArrayList. Here is my code:

public int[] getDestSets()
{
    int[] array = new int[destSet.size()];
    destSet.toArray(array);
    return array;
}

destSet is an integer ArrayList. I got the error "The method toArray(T[]) in the type ArrayList is not applicable for the arguments (int[])". Can anyone give me a hint? Thanks!

ArrayList can only hold Objects not primitives. So it is actuallay ArrayList<Integer> and not int. You need a cast to (int[]) — HectorLector
– HectorLector, Commented Jul 21, 2013 at 23:15
may I ask why you need to return an array of int? Arrays should be avoided unless you're dealing with code you don't control that requires it, in which case you should hide that code under an interface that deals with collections. — sjr
– sjr, Commented Jul 21, 2013 at 23:22

user2264310 · Accepted Answer · 2013-07-22 01:03:01Z

1

You can try use the ArrayUtils class from the Apache Commons Lang library. It will need two steps. First convert the ArrayList to the wrapper object array (Integer[]). After that you can use ArrayUtils.toPrimitive() to convert it to an array of int (int[]).

answered Jul 22, 2013 at 1:03

user2264310

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Community · Accepted Answer · 2017-05-23 12:29:18Z

1

An int[] array cannot be "boxed" to an Integer[] array. You have to use a for-loop. See Why don't Java Generics support primitive types? for more information.

edited May 23, 2017 at 12:29

CommunityBot

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answered Jul 21, 2013 at 23:15

morpheus05

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Comments

Bohemian · Accepted Answer · 2013-07-21 23:28:34Z

1

While the wrapper class Integer will be auto unboxed to an int primitive, arrays/Lists are not auto unboxed to arrays of int.

You must do it the hard way:

public int[] getDestSets() {
    int[] array = new int[destSet.size()];
    int x = 0;
    for (Integer i : destSet)
       array[x++] = i;
    return array;
}

answered Jul 21, 2013 at 23:28

Bohemian♦

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