How do I remove objects from an array in Java?

Question

Given an array of n Objects, let's say it is an array of strings, and it has the following values:

foo[0] = "a";
foo[1] = "cc";
foo[2] = "a";
foo[3] = "dd";

What do I have to do to delete/remove all the strings/objects equal to "a" in the array?

Answer 1

It depends on what you mean by "remove"? An array is a fixed size construct - you can't change the number of elements in it. So you can either a) create a new, shorter, array without the elements you don't want or b) assign the entries you don't want to something that indicates their 'empty' status; usually null if you are not working with primitives.

In the first case create a List from the array, remove the elements, and create a new array from the list. If performance is important iterate over the array assigning any elements that shouldn't be removed to a list, and then create a new array from the list. In the second case simply go through and assign null to the array entries.

Answer 2

I realise this is a very old post, but some of the answers here helped me out, so here's my tuppence' ha'penny's worth!

I struggled getting this to work for quite a while before before twigging that the array that I'm writing back into needed to be resized, unless the changes made to the ArrayList leave the list size unchanged.

If the ArrayList that you're modifying ends up with greater or fewer elements than it started with, the line List.toArray() will cause an exception, so you need something like List.toArray(new String[] {}) or List.toArray(new String[0]) in order to create an array with the new (correct) size.

Sounds obvious now that I know it. Not so obvious to an Android/Java newbie who's getting to grips with new and unfamiliar code constructs and not obvious from some of the earlier posts here, so just wanted to make this point really clear for anybody else scratching their heads for hours like I was!

Answer 3

Arrgh, I can't get the code to show up correctly. Sorry, I got it working. Sorry again, I don't think I read the question properly.

String  foo[] = {"a","cc","a","dd"},
remove = "a";
boolean gaps[] = new boolean[foo.length];
int newlength = 0;

for (int c = 0; c<foo.length; c++)
{
    if (foo[c].equals(remove))
    {
        gaps[c] = true;
        newlength++;
    }
    else 
        gaps[c] = false;

    System.out.println(foo[c]);
}

String newString[] = new String[newlength];

System.out.println("");

for (int c1=0, c2=0; c1<foo.length; c1++)
{
    if (!gaps[c1])
    {
        newString[c2] = foo[c1];
        System.out.println(newString[c2]);
        c2++;
    }
}

Answer 4

Initial array

   int[] array = {5,6,51,4,3,2};

if you want remove 51 that is index 2, use following

 for(int i = 2; i < array.length -1; i++){
    array[i] = array[i + 1];
  }

Answer 5

Use:

list.removeAll(...);
//post what char you need in the ... section

Answer 6

Assign null to the array locations.