java.util

Class EnumSet<T>

public abstract class EnumSet<T extends Enum<T>> extends AbstractSet<T> implements Cloneable, Serializable

Provides an efficient mechanism for recording a set of enumeration constants. As enumerations have a known set of possible values, certain assumptions can be made when creating a set of constants. The maximum size of the set will always be equal to the number of constants, and each value will always be one of these constants. As a result, the set only needs to store whether a particular constant is present or not rather than the values themselves. Each constant can thus be represented by a single bit.

This class is designed to provide an alternative to using integer bit flags by providing a typesafe Collection interface with an underlying implementation that utilises the assumptions above to give an equivalent level of efficiency. The values in a EnumSet must all be from the same Enum type, which allows the contents to be packed into a bit vector. A containment test is then simply a matter of inspecting the appropriate bit, while addition involves setting the same. Such basic operations take place in constant time.

The Iterator implementation traverses the values in the natural order of the enumeration provided by each constant's Enum#ordinal(). It is weakly consistent and will not throw a ConcurrentModificationException. This means that concurrent changes to the set may or may not be noticeable during traversal.

As is usual with most collections, the set is not synchronized by default. This can be remedied by using the synchronizedSet method. Null elements are not supported and attempts to add one will throw a NullPointerException.

Since: 1.5

Method Summary
static <T extends Enum<T>> EnumSet<T>allOf(Class<T> eltType)
Returns a set for the given enumeration type where all the constants are present.
EnumSet<T>clone()
Returns a clone of the set.
static <T extends Enum<T>> EnumSet<T>complementOf(EnumSet<T> other)
Returns a set which is the inverse of the supplied set.
static <T extends Enum<T>> EnumSet<T>copyOf(EnumSet<T> other)
Returns a clone of the given set.
static <T extends Enum<T>> EnumSet<T>copyOf(Collection<T> other)
Creates an EnumSet using the contents of the given collection.
static <T extends Enum<T>> EnumSet<T>noneOf(Class<T> eltType)
Returns a set for the given enumeration type where none of the constants are present.
static <T extends Enum<T>> EnumSet<T>of(T first)
Creates a new EnumSet populated with the given element.
static <T extends Enum<T>> EnumSet<T>of(T first, T second)
Creates a new EnumSet populated with the given two elements.
static <T extends Enum<T>> EnumSet<T>of(T first, T second, T third)
Creates a new EnumSet populated with the given three elements.
static <T extends Enum<T>> EnumSet<T>of(T first, T second, T third, T fourth)
Creates a new EnumSet populated with the given four elements.
static <T extends Enum<T>> EnumSet<T>of(T first, T second, T third, T fourth, T fifth)
Creates a new EnumSet populated with the given five elements.
static <T extends Enum<T>> EnumSet<T>of(T first, T... rest)
Creates a new EnumSet populated with the given elements.
static <T extends Enum<T>> EnumSet<T>range(T from, T to)
Creates a new EnumSet using the enumeration constants starting from {@code from} and ending at {@code to} inclusive.

Method Detail

allOf

public static <T extends Enum<T>> EnumSet<T> allOf(Class<T> eltType)
Returns a set for the given enumeration type where all the constants are present.

Parameters: eltType the type of enumeration to use for the set.

Returns: an EnumSet with all the bits set.

Throws: NullPointerException if the element type is null.

clone

public EnumSet<T> clone()
Returns a clone of the set.

Returns: a clone of the set.

complementOf

public static <T extends Enum<T>> EnumSet<T> complementOf(EnumSet<T> other)
Returns a set which is the inverse of the supplied set. If a constant is present in the current set, it will not be present in the new set and vice versa.

Parameters: other the set to provide the complement of.

Returns: an EnumSet which is the inverse of the current one.

Throws: NullPointerException if other is null.

copyOf

public static <T extends Enum<T>> EnumSet<T> copyOf(EnumSet<T> other)
Returns a clone of the given set.

Parameters: other the set to clone.

Returns: an EnumSet that is a clone of the given set.

Throws: NullPointerException if other is null.

copyOf

public static <T extends Enum<T>> EnumSet<T> copyOf(Collection<T> other)
Creates an EnumSet using the contents of the given collection. If the collection is also an EnumSet, this method works the same as copyOf. Otherwise, the elements of the collection are inspected and used to populate the new set.

Parameters: other the collection to use to populate the new set.

Returns: an EnumSet containing elements from the given collection.

Throws: NullPointerException if other is null. IllegalArgumentException if the collection is empty.

noneOf

public static <T extends Enum<T>> EnumSet<T> noneOf(Class<T> eltType)
Returns a set for the given enumeration type where none of the constants are present.

Parameters: eltType the type of enumeration to use for the set.

Returns: an EnumSet with none of the bits set.

Throws: NullPointerException if the element type is null.

of

public static <T extends Enum<T>> EnumSet<T> of(T first)
Creates a new EnumSet populated with the given element.

Parameters: first the element to use to populate the new set.

Returns: an EnumSet containing the element.

Throws: NullPointerException if first is null.

of

public static <T extends Enum<T>> EnumSet<T> of(T first, T second)
Creates a new EnumSet populated with the given two elements.

Parameters: first the first element to use to populate the new set. second the second element to use.

Returns: an EnumSet containing the elements.

Throws: NullPointerException if any of the parameters are null.

of

public static <T extends Enum<T>> EnumSet<T> of(T first, T second, T third)
Creates a new EnumSet populated with the given three elements.

Parameters: first the first element to use to populate the new set. second the second element to use. third the third element to use.

Returns: an EnumSet containing the elements.

Throws: NullPointerException if any of the parameters are null.

of

public static <T extends Enum<T>> EnumSet<T> of(T first, T second, T third, T fourth)
Creates a new EnumSet populated with the given four elements.

Parameters: first the first element to use to populate the new set. second the second element to use. third the third element to use. fourth the fourth element to use.

Returns: an EnumSet containing the elements.

Throws: NullPointerException if any of the parameters are null.

of

public static <T extends Enum<T>> EnumSet<T> of(T first, T second, T third, T fourth, T fifth)
Creates a new EnumSet populated with the given five elements.

Parameters: first the first element to use to populate the new set. second the second element to use. third the third element to use. fourth the fourth element to use. fifth the fifth element to use.

Returns: an EnumSet containing the elements.

Throws: NullPointerException if any of the parameters are null.

of

public static <T extends Enum<T>> EnumSet<T> of(T first, T... rest)
Creates a new EnumSet populated with the given elements.

Parameters: first the first element to use to populate the new set. rest the other elements to use.

Returns: an EnumSet containing the elements.

Throws: NullPointerException if any of the parameters are null.

range

public static <T extends Enum<T>> EnumSet<T> range(T from, T to)
Creates a new EnumSet using the enumeration constants starting from {@code from} and ending at {@code to} inclusive. The two may be the same, but they must be in the correct order. So giving the first constant twice would give a set with just that constant set, while supplying the first and second constant will give a set with those two elements. However, specifying the second as the {@code from} element followed by an earlier element as the {@code to} element will result in an error.

Parameters: from the element to start from. to the element to end at (may be the same as {@code from}.

Returns: an EnumSet containing the specified range of elements.

Throws: NullPointerException if any of the parameters are null. IllegalArgumentException if {@code first.compareTo(last) > 0}.