Array Lists in java

Question

Is there a way to remove all empty cells in an ArrayList by just a built in function call? I saw trimToSize but I didn't really get what it meant.

For example, suppose I have an array that contains {1,2,3}. Lets say I say array.remove(1) so now the array looks like {1,null,3}. Is there a function to call to make it converge to be {1,3}?

I know I can hard code a method to do that for me but I was just curious.

Are you talking about an array (eg., int[] foo = ...) or an ArrayList (eg., ArrayList<Integer> = ...)? — Greg
– Greg, Commented Mar 25, 2011 at 16:22
The word ArrayList is not a random Java term representing an array. It's a real Java class with real methods! Start here to learn about it: download.oracle.com/javase/tutorial/collections/index.html — BalusC
– BalusC, Commented Mar 25, 2011 at 16:24
I think trimToSize is doing just what you want. It set's the capacity to be the same as the size. — Mojo Risin
– Mojo Risin, Commented Mar 25, 2011 at 16:28
An edit to this question changed it to refer to ArrayList, but from the original question it was not clear whether au789 was talking about an array or an ArrayList. — Greg
– Greg, Commented Mar 25, 2011 at 16:29

Jonathon Faust · Accepted Answer · 2011-03-25 18:03:57Z

7

That's exactly what remove does.

Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).

Now, if you're talking about arrays, not ArrayList, the answer is no.

edited Mar 25, 2011 at 18:03

answered Mar 25, 2011 at 16:22

Jonathon Faust

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au789 Over a year ago

Thanks, I'll be sure to accept your answer here shortly. I'm relatively new so I didn't know array lists automatically handled any shifting.

Greg · Accepted Answer · 2011-03-25 16:23:56Z

2

If you are using an ArrayList, you don't need to worry about compacting the array after removing an element from it. The ArrayList class takes care of this kind of housekeeping.

If you are using an array, you could use the Commons Lang ArrayUtils class. The removeElement methods in this class simplify removing an element from an array and shifting all elements after it to the left.

answered Mar 25, 2011 at 16:23

Greg

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Comments

Bartzilla · Accepted Answer · 2011-03-25 16:52:38Z

1

In here you find a post that shows how to remove all null elements in a Collection

    List<Integer> myList = new ArrayList<Integer>();

    myList.add(1);
    myList.add(2);
    myList.add(null);
    myList.add(3);
    myList.add(null);
    myList.add(4);

    System.out.println("With null values");
    for(Integer i: myList)
        System.out.println(i);

    myList.removeAll(Collections.singleton(null));              

    System.out.println("After deleting null values");
    for(Integer i: myList)
        System.out.println(i);

Output: With null values 1 2 null 3 null 4

After deleting null values 1 2 3 4

edited Mar 25, 2011 at 16:52

answered Mar 25, 2011 at 16:25

Bartzilla

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1 Comment

Aleadam Over a year ago

+1 for the myList.removeAll(Collections.singleton(null)); line. You learn every day a new thing in SO :)

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