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I'm trying to use in place of bitmask below is the code
public static Set<Amenities> fromBitFlags(int bitFlag) { return ALL_OPTS.stream().filter(a -> (a.ameityId & bitFlag) > 0).collect(Collectors.toSet()); } I would like to return EnumSet instead of a plain set(dont want to loose out on EnumSet's usefulness just because of casting).
Need some directions on how to create a Custom Collector to collect EnumSet.
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collect() Method. Stream. collect() is one of the Java 8's Stream API's terminal methods. It allows us to perform mutable fold operations (repackaging elements to some data structures and applying some additional logic, concatenating them, etc.) on data elements held in a Stream instance.
EnumSet. noneOf(Class elementType ) method in Java is used to create a null set of the type elementType. Syntax: public static <E extends Enum<E>> EnumSet<E> noneOf(Class<E> elementType)
An immutable list is created this way. List<Person> immutableList = Collections. unmodifiableList(new ArrayList<>(persons)); This creates an immutable list since a conversion constructor is being used.
toList() returns an immutable list. So, trying to add a new element to the list will simply lead to UnsupportedOperationException.
You may use toCollection(Supplier):
return ALL_OPTS.stream().filter(a -> (a.ameityId & bitFlag) > 0) .collect(Collectors.toCollection(() -> EnumSet.noneOf(Amenities.class))); The toCollection method receives a lambda which should create an empty collection to store the result. Here we create empty EnumSet using EnumSet.noneOf call. Note that for EnumSet you must always specify (implicitly or explicitly) which enum is this set for.
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