List<String> list = Collections.singletonList("E")
Map<String,String> map = Collections.singletonMap("field3", "value3");
Set<String> set = Collections.singleton("Hello");

List<String> list =  List.of("e")
Map<String,String> map = Map.of"field3", "value3");
Set<String> set  = Set.of("Hello");