Merging two arrayLists into a new arrayList, with no duplicates and in order, in Java

Question

I am trying to \"combine\" two arrayLists, producing a new arrayList that contains all the numbers in the two combined arrayLists, but without any duplicate elements and the

Answer 1

Java 8 Stream API can be used for the purpose,

ArrayList list1 = new ArrayList<>();

list1.add("A");
list1.add("B");
list1.add("A");
list1.add("D");
list1.add("G");

ArrayList list2 = new ArrayList<>();

list2.add("B");
list2.add("D");
list2.add("E");
list2.add("G");

List noDup = Stream.concat(list1.stream(), list2.stream())
                     .distinct()
                     .collect(Collectors.toList());
noDup.forEach(System.out::println);

En passant, it shouldn't be forgetten that distinct() makes use of hashCode().