Operator - Contains

determine whether an Observable emits a particular item or not

Pass the Contains operator a particular item, and the Observable it returns will emit true if that item is emitted by the source Observable, or false if the source Observable terminates without emitting that item.

A related operator, IsEmpty returns an Observable that emits true if and only if the source Observable completes without emitting any items. It emits false if the source Observable emits an item.

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 List<Integer> list2 = new ArrayList<>();
 list2.add(1);
 list2.add(2);
 list2.add(3);
 list2.add(4);
 list2.add(5);

 Observable.fromIterable(list2).contains(3).subscribe(System.out::println);

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