java11-enumset

Overview of EnumSet API.

Reference: https://docs.oracle.com/javase/10/docs/api/java/util/EnumSet.html

preface

EnumSet is specialized Set implementation for use with enum types.

Enum sets are represented internally as bit vectors. This representation is extremely compact and efficient. The space and time performance of this class should be good enough to allow its use as a high-quality, typesafe alternative to traditional int-based "bit flags." (for bit flags please refer my other github project: https://github.com/mtumilowicz/java11-ORed-container)

Even bulk operations (such as containsAll and retainAll) should run very quickly if their argument is also an enum set.

The returned iterator (from iterator()) is weakly consistent (for iterator types please refer my other github project: https://github.com/mtumilowicz/java-iterator-fail-types).

Null elements are not permitted (NPE).

static methods

Assumption: <E extends Enum<E>>

• EnumSet<E> allOf​(Class<E> elementType) - Creates an enum set containing all of the elements in the specified element type.
• EnumSet<E> complementOf​(EnumSet<E> s) - Creates an enum set with the same element type as the specified enum set, initially containing all the elements of this type that are not contained in the specified set.
• EnumSet<E> copyOf​(Collection<E> c) - Creates an enum set initialized from the specified collection.
• EnumSet<E> copyOf​(EnumSet<E> s) - Creates an enum set with the same element type as the specified enum set, initially containing the same elements (if any).
• EnumSet<E> noneOf​(Class<E> elementType) - Creates an empty enum set with the specified element type.
• EnumSet<E> of​(E e) - Creates an enum set initially containing the specified element. Up to five elements.
• EnumSet<E> range​(E from, E to) - Creates an enum set initially containing all of the elements in the range defined by the two specified endpoints.

summary

• All basic operations execute in constant time. They are likely (though not guaranteed) to be much faster than their HashSet counterparts. Even bulk operations execute in constant time if their argument is also an enum set.

• Please note that from static methods we obtain mutable set.

project description

We provide tests for static methods:

• allOf

  EnumSet<DayOfWeek> dayOfWeeks = EnumSet.allOf(DayOfWeek.class);
  
  assertThat(dayOfWeeks.size(), is(7));
  assertThat(dayOfWeeks, contains(
          DayOfWeek.MONDAY,
          DayOfWeek.TUESDAY,
          DayOfWeek.WEDNESDAY,
          DayOfWeek.THURSDAY,
          DayOfWeek.FRIDAY,
          DayOfWeek.SATURDAY,
          DayOfWeek.SUNDAY)
  );
  

• complementOf

  EnumSet<DayOfWeek> withoutWeekendDays = EnumSet.complementOf(
          EnumSet.of(DayOfWeek.SATURDAY, DayOfWeek.SUNDAY)
  );
  
  assertThat(withoutWeekendDays.size(), is(5));
  assertThat(withoutWeekendDays, contains(
          DayOfWeek.MONDAY,
          DayOfWeek.TUESDAY,
          DayOfWeek.WEDNESDAY,
          DayOfWeek.THURSDAY,
          DayOfWeek.FRIDAY)
  );
  

• range

  EnumSet<DayOfWeek> workingDays = EnumSet.range(DayOfWeek.MONDAY, DayOfWeek.FRIDAY);
  
  assertThat(workingDays.size(), is(5));
  assertThat(workingDays, contains(
          DayOfWeek.MONDAY,
          DayOfWeek.TUESDAY,
          DayOfWeek.WEDNESDAY,
          DayOfWeek.THURSDAY,
          DayOfWeek.FRIDAY)
  );
  

• noneOf

  EnumSet<DayOfWeek> emptyDays = EnumSet.noneOf(DayOfWeek.class);
  
  assertTrue(emptyDays.isEmpty());
  
  emptyDays.add(DayOfWeek.SATURDAY);
  
  assertThat(emptyDays, contains(DayOfWeek.SATURDAY));