How to compare two array list and extract the element in third array list that are not common in both

Question

I have two arraylist that has some elements I am comparing the elements of both arraylists and trying to extract the elements in third arraylist that are not common in both lists.

This is what I have done so far:

public class Details
{
   public static void main(String [] args)
    {

      ArrayList<String> al1= new ArrayList<String>();
      al1.add("hi");
      al1.add("How are you");
      al1.add("Good Morning");
      al1.add("bye");
      al1.add("Good night");

      ArrayList<String> al2= new ArrayList<String>();
      al2.add("Howdy");
      al2.add("Good Evening");
      al2.add("bye");
      al2.add("Good night");

      //Storing the comparison output in ArrayList<String>
      ArrayList<String> al3= new ArrayList<String>();
      for (String temp : al1)
          al3.add(al2.contains(temp) ? "Yes" : "No");
      System.out.println(al3);

  }
}

OUTPUT

[No, No, No, Yes, Yes]

I don't want output in yes or no form I want elements in new array list that are no common in both lists.

Someone please let me know how can I achieve desired result. Any help would be appreciated.

THANKS

Elliott Frisch · Accepted Answer · 2019-07-28 05:59:05Z

First, please program to the List interface (instead of the ArrayList concrete type). You can also use Arrays.asList to shorten your initialization. I would then stream() each List - you want fo filter the stream for elements not contained in the other List and then add them to your third List. Something like,

List<String> al1 = Arrays.asList("hi", "How are you", "Good Morning", "bye", "Good night");
List<String> al2 = Arrays.asList("Howdy", "Good Evening", "bye", "Good night");
List<String> al3 = al1.stream().filter(s -> !al2.contains(s)).collect(Collectors.toList());
al3.addAll(al2.stream().filter(s -> !al1.contains(s)).collect(Collectors.toList()));
System.out.println(al3);

Which outputs

[hi, How are you, Good Morning, Howdy, Good Evening]

or, without streams (so you can better understand the algorithm),

List<String> al3 = new ArrayList<>();
for (String s : al1) {
    if (!al2.contains(s)) {
        al3.add(s);
    }
}
for (String s : al2) {
    if (!al1.contains(s)) {
        al3.add(s);
    }
}
System.out.println(al3);

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