Check ArrayList content with Java stream

Use filters

List<Object> objLst = new ArrayList<Object>(Arrays.asList(new Object[] {new User(), new Person(), new Dummy() }));

return (objLst.stream()
    .filter(e -> !(e instanceof User || e instanceof Person))
    .limit(1)
    .count() > 0) ? null : objLst;

Alternative to Paul's answer (with the if-else in your question)

if (arrayList.stream().allMatch(o -> o instanceof Person || o instanceof User)) {
    return null;
} else {
    return arrayList;
}

Assuming Person and User are types, rather than specific objects, you can do something like this.

return list.stream()
           .filter(o -> !(o instanceof Person) && !(o instanceof User))
           .findAny()
           .isPresent() ? list : null;