Module java.base
Package java.util

Class EnumSet<E extends Enum<E>>

java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractSet<E>
java.util.EnumSet<E>
Type Parameters:
E - the enum type of elements maintained by this set
All Implemented Interfaces:
Serializable, Cloneable, Iterable<E>, Collection<E>, Set<E>
public abstract sealed class EnumSet<E extends Enum<E>> extends AbstractSet<E> implements Cloneable, Serializable
A specialized Set implementation for use with enum types. All of the elements in an enum set must come from a single enum type that is specified, explicitly or implicitly, when the set is created. 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." Even bulk operations (such as containsAll and retainAll) should run very quickly if their argument is also an enum set.

The iterator returned by the iterator method traverses the elements in their natural order (the order in which the enum constants are declared). The returned iterator is weakly consistent: it will never throw ConcurrentModificationException and it may or may not show the effects of any modifications to the set that occur while the iteration is in progress.

Null elements are not permitted. Attempts to insert a null element will throw NullPointerException. Attempts to test for the presence of a null element or to remove one will, however, function properly.

Like most collection implementations, EnumSet is not synchronized. If multiple threads access an enum set concurrently, and at least one of the threads modifies the set, it should be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the enum set. If no such object exists, the set should be "wrapped" using the Collections.synchronizedSet(java.util.Set<T>) method. This is best done at creation time, to prevent accidental unsynchronized access: 

 Set<MyEnum> s = Collections.synchronizedSet(EnumSet.noneOf(MyEnum.class));

Implementation note: 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.

This class is a member of the Java Collections Framework.

Since:
1.5
See Also:

  • Method Details

    • noneOf

      public static <E extends Enum<E>> EnumSet<E> noneOf(Class<E> elementType)
      Creates an empty enum set with the specified element type.
      Type Parameters:
      E - The class of the elements in the set
      Parameters:
      elementType - the class object of the element type for this enum set
      Returns:
      An empty enum set of the specified type.
      Throws:
      NullPointerException - if elementType is null

    • allOf

      public static <E extends Enum<E>> EnumSet<E> allOf(Class<E> elementType)
      Creates an enum set containing all of the elements in the specified element type.
      Type Parameters:
      E - The class of the elements in the set
      Parameters:
      elementType - the class object of the element type for this enum set
      Returns:
      An enum set containing all the elements in the specified type.
      Throws:
      NullPointerException - if elementType is null

    • copyOf

      public static <E extends Enum<E>> 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).
      Type Parameters:
      E - The class of the elements in the set
      Parameters:
      s - the enum set from which to initialize this enum set
      Returns:
      A copy of the specified enum set.
      Throws:
      NullPointerException - if s is null

    • copyOf

      public static <E extends Enum<E>> EnumSet<E> copyOf(Collection<E> c)
      Creates an enum set initialized from the specified collection. If the specified collection is an EnumSet instance, this static factory method behaves identically to copyOf(EnumSet). Otherwise, the specified collection must contain at least one element (in order to determine the new enum set's element type).
      Type Parameters:
      E - The class of the elements in the collection
      Parameters:
      c - the collection from which to initialize this enum set
      Returns:
      An enum set initialized from the given collection.
      Throws:
      IllegalArgumentException - if c is not an EnumSet instance and contains no elements
      NullPointerException - if c is null

    • complementOf

      public static <E extends Enum<E>> 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.
      Type Parameters:
      E - The class of the elements in the enum set
      Parameters:
      s - the enum set from whose complement to initialize this enum set
      Returns:
      The complement of the specified set in this set
      Throws:
      NullPointerException - if s is null

    • of

      public static <E extends Enum<E>> EnumSet<E> of(E e)
      Creates an enum set initially containing the specified element. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.
      Type Parameters:
      E - The class of the specified element and of the set
      Parameters:
      e - the element that this set is to contain initially
      Returns:
      an enum set initially containing the specified element
      Throws:
      NullPointerException - if e is null

    • of

      public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2)
      Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.
      Type Parameters:
      E - The class of the parameter elements and of the set
      Parameters:
      e1 - an element that this set is to contain initially
      e2 - another element that this set is to contain initially
      Returns:
      an enum set initially containing the specified elements
      Throws:
      NullPointerException - if any parameters are null

    • of

      public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2, E e3)
      Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.
      Type Parameters:
      E - The class of the parameter elements and of the set
      Parameters:
      e1 - an element that this set is to contain initially
      e2 - another element that this set is to contain initially
      e3 - another element that this set is to contain initially
      Returns:
      an enum set initially containing the specified elements
      Throws:
      NullPointerException - if any parameters are null

    • of

      public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2, E e3, E e4)
      Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.
      Type Parameters:
      E - The class of the parameter elements and of the set
      Parameters:
      e1 - an element that this set is to contain initially
      e2 - another element that this set is to contain initially
      e3 - another element that this set is to contain initially
      e4 - another element that this set is to contain initially
      Returns:
      an enum set initially containing the specified elements
      Throws:
      NullPointerException - if any parameters are null

    • of

      public static <E extends Enum<E>> EnumSet<E> of(E e1, E e2, E e3, E e4, E e5)
      Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.
      Type Parameters:
      E - The class of the parameter elements and of the set
      Parameters:
      e1 - an element that this set is to contain initially
      e2 - another element that this set is to contain initially
      e3 - another element that this set is to contain initially
      e4 - another element that this set is to contain initially
      e5 - another element that this set is to contain initially
      Returns:
      an enum set initially containing the specified elements
      Throws:
      NullPointerException - if any parameters are null

    • of

      @SafeVarargs public static <E extends Enum<E>> EnumSet<E> of(E first, E... rest)
      Creates an enum set initially containing the specified elements. This factory, whose parameter list uses the varargs feature, may be used to create an enum set initially containing an arbitrary number of elements, but it is likely to run slower than the overloadings that do not use varargs.
      Type Parameters:
      E - The class of the parameter elements and of the set
      Parameters:
      first - an element that the set is to contain initially
      rest - the remaining elements the set is to contain initially
      Returns:
      an enum set initially containing the specified elements
      Throws:
      NullPointerException - if any of the specified elements are null, or if rest is null

    • range

      public static <E extends Enum<E>> 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. The returned set will contain the endpoints themselves, which may be identical but must not be out of order.
      Type Parameters:
      E - The class of the parameter elements and of the set
      Parameters:
      from - the first element in the range
      to - the last element in the range
      Returns:
      an enum set initially containing all of the elements in the range defined by the two specified endpoints
      Throws:
      NullPointerException - if from or to are null
      IllegalArgumentException - if from.compareTo(to) > 0

    • clone

      public EnumSet<E> clone()
      Returns a copy of this set.
      Overrides:
      clone in class Object
      Returns:
      a copy of this set
      See Also: