Records: defensive copies keep a record truly immutable

record Team(String name, List<String> members) {
    Team(String name, List<String> members) {
        this.name = name;
        this.members = List.copyOf(members);      // snapshot on the way in
    }
}

var source = new ArrayList<>(List.of("Ava", "Ben"));
var team = new Team("core", source);
source.add("Intruder");

System.out.println("record kept its own copy: " + team.members());
try {
    team.members().add("Nope");
} catch (UnsupportedOperationException e) {
    System.out.println("and the exposed list is unmodifiable");
}

record kept its own copy: [Ava, Ben]
and the exposed list is unmodifiable