Package com.google.common.collect

Class ImmutableSet<E>

  • All Implemented Interfaces:
    Serializable, Iterable<E>, Collection<E>, Set<E>
    Direct Known Subclasses:
    ImmutableSortedSet
    @GwtCompatible(serializable=true,
               emulated=true)
public abstract class ImmutableSet<E>
extends ImmutableCollection<E>
implements Set<E>
    A high-performance, immutable Set with reliable, user-specified iteration order. Does not permit null elements.

    Unlike Collections.unmodifiableSet(java.util.Set<? extends T>), which is a view of a separate collection that can still change, an instance of this class contains its own private data and will never change. This class is convenient for public static final sets ("constant sets") and also lets you easily make a "defensive copy" of a set provided to your class by a caller.

    Warning: Like most sets, an ImmutableSet will not function correctly if an element is modified after being placed in the set. For this reason, and to avoid general confusion, it is strongly recommended to place only immutable objects into this collection.

    This class has been observed to perform significantly better than HashSet for objects with very fast Object.hashCode() implementations (as a well-behaved immutable object should). While this class's factory methods create hash-based instances, the ImmutableSortedSet subclass performs binary searches instead.

    Note: Although this class is not final, it cannot be subclassed outside its package as it has no public or protected constructors. Thus, instances of this type are guaranteed to be immutable.

    See the Guava User Guide article on immutable collections.

    Since:
    2.0 (imported from Google Collections Library)
    See Also:
    ImmutableList, ImmutableMap, Serialized Form

    • Method Detail

      • of

        public static <E> ImmutableSet<E> of()
        Returns the empty immutable set. This set behaves and performs comparably to Collections.emptySet(), and is preferable mainly for consistency and maintainability of your code.

      • of

        public static <E> ImmutableSet<E> of​(E element)
        Returns an immutable set containing a single element. This set behaves and performs comparably to Collections.singleton(T), but will not accept a null element. It is preferable mainly for consistency and maintainability of your code.

      • of

        public static <E> ImmutableSet<E> of​(E e1,
                                     E e2,
                                     E e3,
                                     E e4,
                                     E e5,
                                     E e6,
                                     E... others)
        Returns an immutable set containing the given elements, in order. Repeated occurrences of an element (according to Object.equals(java.lang.Object)) after the first are ignored.
        Throws:
        NullPointerException - if any element is null
        Since:
        3.0 (source-compatible since 2.0)

      • copyOf

        public static <E> ImmutableSet<E> copyOf​(E[] elements)
        Returns an immutable set containing the given elements, in order. Repeated occurrences of an element (according to Object.equals(java.lang.Object)) after the first are ignored.
        Throws:
        NullPointerException - if any of elements is null
        Since:
        3.0

      • copyOf

        public static <E> ImmutableSet<E> copyOf​(Iterable<? extends E> elements)
        Returns an immutable set containing the given elements, in order. Repeated occurrences of an element (according to Object.equals(java.lang.Object)) after the first are ignored. This method iterates over elements at most once.

        Note that if s is a Set<String>, then ImmutableSet.copyOf(s) returns an ImmutableSet<String> containing each of the strings in s, while ImmutableSet.of(s) returns a ImmutableSet<Set<String>> containing one element (the given set itself).

        Despite the method name, this method attempts to avoid actually copying the data when it is safe to do so. The exact circumstances under which a copy will or will not be performed are undocumented and subject to change.

        Throws:
        NullPointerException - if any of elements is null

      • copyOf

        public static <E> ImmutableSet<E> copyOf​(Collection<? extends E> elements)
        Returns an immutable set containing the given elements, in order. Repeated occurrences of an element (according to Object.equals(java.lang.Object)) after the first are ignored. This method iterates over elements at most once.

        Note that if s is a Set<String>, then ImmutableSet.copyOf(s) returns an ImmutableSet<String> containing each of the strings in s, while ImmutableSet.of(s) returns a ImmutableSet<Set<String>> containing one element (the given set itself).

        Note: Despite what the method name suggests, copyOf will return constant-space views, rather than linear-space copies, of some inputs known to be immutable. For some other immutable inputs, such as key sets of an ImmutableMap, it still performs a copy in order to avoid holding references to the values of the map. The heuristics used in this decision are undocumented and subject to change except that:

        • A full copy will be done of any ImmutableSortedSet.
        • ImmutableSet.copyOf() is idempotent with respect to pointer equality.

        This method is safe to use even when elements is a synchronized or concurrent collection that is currently being modified by another thread.

        Throws:
        NullPointerException - if any of elements is null
        Since:
        7.0 (source-compatible since 2.0)