Compare two ArrayList(); and delete the different elements

Question

i wanted to compare two ArrayList arrays and delete the different elements.

List<String> al1 = new ArrayList<String>();
List<String> al2 = new ArrayList<String>();

al1.add("222");

al2.add("222");
al2.add("333");

System.out.println(al1);
System.out.println(al2);

The output of println is:

[222]
[222, 333]

I want to remove the 333 in the second array because it is not in the first one how can i achieve this ?

Thanks in advance.

by writing the code that does that. what have you tried so far? — Stultuske, Feb 22 '18 at 10:01
You are expected to do *serious* prior posting questions. What makes you think that you are the *first* person on wondering how to do things like that? — GhostCat, Feb 22 '18 at 10:03

Marteng · Answer 1 · 2018-02-22T14:59:25.143

0

You can do this with java.util.List.retainAll(Collection<?>):

public static void main(String[] args) {
   List<String> al1 = new ArrayList<String>();
   List<String> al2 = new ArrayList<String>();

   al1.add("222");

   al2.add("222");
   al2.add("333");

   al1.retainAll(al2);
   al2.retainAll(al1); // See Stultuske's comment.
   System.out.println(al1);
   System.out.println(al2);
}

edited Feb 22 '18 at 14:59

answered Feb 22 '18 at 10:02

Marteng

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and what are you forgetting in this example? – Stultuske Feb 22 '18 at 10:03
@Stultuske, tell me :) – Marteng Feb 22 '18 at 10:04
2

al2.retainAll(al1); ;) for all we know, the extra variable in a next run is in al2, so you need to go retainAll on both – Stultuske Feb 22 '18 at 10:05
Thank you very much Marteng & Stultuske.. thought that it would be harder . – Computer85 Feb 22 '18 at 10:33

Compare two ArrayList(); and delete the different elements

1 Answers1