Delete int[] from ArrayList<int[]>

Question

Hi, I'm trying to delete an int[] from an ArrayList. Due to my code I only have the values so I'm creating the array and then call remove();

int[] pos = new int[]{0,1};
positionList.remove(pos);

positionList is the corrisponding ArrayList

This actually doesn't work. Is there another possibility than iterating through the list like

for (int[] pos : positionList) {
  if (posX == pos[0] && posY == pos[1]) {
    positionList.remove(pos);
    break;
  }
}

Answer 1

Looking at the posX and posY, I'm curious if something like ArrayList<Point> is a better solution for you.

The reason the remove couldn't find the array is because the new array is not equals to the array already in the collection.

(new int[0]).equals(new int[0]) // false!

If you create you own Point class, then you can @Override equals to behave as you want, and you can simply call remove(new Point(posX, posY)).

You should also consider having a Set<Point> positionList instead, because implementations offer much faster removal (O(1) for HashSet, O(log N) for TreeSet). Remember to @Override hashCode (which you have to do anyway if you @Override equals), and make Point implements Comparable<Point> (or provide an external Comparator<Point>) if you want to use TreeSet or need to sort the points in other contexts.

If your int[] has many elements and a custom Point class is not applicable, then you may want to consider switching to List<Integer> instead (see also: Effective Java 2nd Edition, item 25: prefer lists to arrays). It has the equals behavior that you need. It is slower, but it may still be fast enough.

Lastly, if you insist on using int[], you can just wrap it inside your own IntArray class, and have a ArrayList<IntArray> instead. @Override equals and hashCode to use Arrays.equals(int[], int[]), and hashCode(int[]) respectively.

Answer 2

It's a bad practice to use arrays for holding data that isn't a sequence of items, literally.

Your array is actually a data holder with two distinct feilds. Define a coordinates class and override Object.equals(Object). Then your code will become much cleaner:

ArrayList<MyPoint> positionList;
// fill list
MyPoint testPos = new MyPoint(0, 1);
positionList.remove(testPos);

You should be guessing how to define MyPoint..