CODEWITHSUNDEEP
javalistjava-8
Deepak Shajan
Deepak Shajan

Reputation: 921

AND/OR operations on lists in Java

Let consider two arraylists.

ArrayList<Integer> list1 = new ArrayList<Integer>();
list1.add(1);
list1.add(2);
list1.add(3);

ArrayList<Integer> list2 = new ArrayList<Integer>();
list2.add(3);
list2.add(4);
list2.add(5);

I want to perform AND and OR operation between these lists. For example, here when I perform AND operation b/w list1 & list2 output should be a list containing only 3 when I perform OR operation b/w list1 & list2 output should be a list containing 1,2,3,4,5(not 3 repeating twice).

Is there any possibility in Java to achieve this scenario? Can we use Java 8 Streams in this case? Please give me the most efficient way to get the answer.

Upvotes: 2

Views: 267

Answers (4)

aioobe
aioobe

Reputation: 421170

Using the Stream API:

List<Integer> union = Stream.concat(list1.stream(), list2.stream())
                            .distinct()
                            .collect(Collectors.toList());


List<Integer> intersection = list1.stream()
                                  .filter(list2::contains)
                                  .collect(Collectors.toList());

Without the Stream API:

List<Integer> intersection = new ArrayList<>(list1);
intersection.retainAll(list2);


List<Integer> union = new ArrayList<>(list1);
List<Integer> toAdd = new ArrayList<>(list2);
toAdd.removeAll(list1);  // avoid duplicates
union.addAll(toAdd);

Upvotes: 5

Subbu
Subbu

Reputation: 308

It could be useful:

Set<Integer> orSet = new HashSet<Integer>();
    orSet.addAll(list);
    orSet.addAll(list1);
    List<Integer> orList = new ArrayList<Integer>(orSet);
    List<Integer> andList = new ArrayList<Integer>();
    int i=0;
    Iterator<Integer> itr = list.iterator();
    while(itr.hasNext()){
        int v = itr.next();
        if(list1.contains(v)){
            andList.add(v);
        }
    }

    System.out.println(orList);
    System.out.println(andList);

Upvotes: 1

Konstantin Yovkov
Konstantin Yovkov

Reputation: 62874

If you really insist on Streams, here's what you can do:

For the AND, you can do:

List<Integer> AND = list1.stream()
                         .filter(list2:contains)
                         .collect(Collectors.toList());

For the OR, you can do:

List<Integer> OR =  Arrays.asList(list1, list2)
                         .stream()
                         .flatMap(List::stream)
                         .distinct()
                         .collect(Collectors.toList());

or even better, as suggested by @Alexis C. and inspired by @aioobe:

List<Integer> OR = Stream.concat(list1.stream(), list2.stream())
                         .distinct()
                         .collect(Collectors.toList());

Upvotes: 1

Kayaman
Kayaman

Reputation: 73568

You need to use Sets to avoid duplicates. Then it's just a matter of using addAll(), removeAll() and retainAll() operations.

Upvotes: 2

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