com.google.common.collect

Class ImmutableSet<E>

java.lang.Object

com.google.common.collect.ImmutableCollection<E>

com.google.common.collect.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)

Author:

Kevin Bourrillion, Nick Kralevich

See Also:

ImmutableList, ImmutableMap, Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ImmutableSet.Builder<E> A builder for creating immutable set instances, especially public static final sets ("constant sets").

Method Summary

Methods

Modifier and Type	Method and Description
static <E> ImmutableSet.Builder<E>	builder() Returns a new builder.
static <E> ImmutableSet<E>	copyOf(Collection<? extends E> elements) Returns an immutable set containing the given elements, in order.
static <E> ImmutableSet<E>	copyOf(E[] elements) Returns an immutable set containing the given elements, in order.
static <E> ImmutableSet<E>	copyOf(Iterable<? extends E> elements) Returns an immutable set containing the given elements, in order.
static <E> ImmutableSet<E>	copyOf(Iterator<? extends E> elements) Returns an immutable set containing the given elements, in order.
boolean	equals(Object object)
int	hashCode()
abstract UnmodifiableIterator<E>	iterator() Returns an unmodifiable iterator across the elements in this collection.
static <E> ImmutableSet<E>	of() Returns the empty immutable set.
static <E> ImmutableSet<E>	of(E element) Returns an immutable set containing a single element.
static <E> ImmutableSet<E>	of(E e1, E e2) Returns an immutable set containing the given elements, in order.
static <E> ImmutableSet<E>	of(E e1, E e2, E e3) Returns an immutable set containing the given elements, in order.
static <E> ImmutableSet<E>	of(E e1, E e2, E e3, E e4) Returns an immutable set containing the given elements, in order.
static <E> ImmutableSet<E>	of(E e1, E e2, E e3, E e4, E e5) Returns an immutable set containing the given elements, in order.
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.

Methods inherited from class com.google.common.collect.ImmutableCollection

add, addAll, asList, clear, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Set

add, addAll, clear, contains, containsAll, isEmpty, remove, removeAll, retainAll, size, toArray, toArray

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)

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

of

public static <E> ImmutableSet<E> of(E e1,
                     E e2,
                     E e3)

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

of

public static <E> ImmutableSet<E> of(E e1,
                     E e2,
                     E e3,
                     E e4)

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

of

public static <E> ImmutableSet<E> of(E e1,
                     E e2,
                     E e3,
                     E e4,
                     E e5)

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

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(Iterator<? 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.

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)

equals

public boolean equals(@Nullable
             Object object)

Specified by:

equals in interface Collection<E>

Specified by:

equals in interface Set<E>

Overrides:

equals in class Object

hashCode

public int hashCode()

Specified by:

hashCode in interface Collection<E>

Specified by:

hashCode in interface Set<E>

Overrides:

hashCode in class Object

iterator

public abstract UnmodifiableIterator<E> iterator()

Description copied from class: ImmutableCollection

Returns an unmodifiable iterator across the elements in this collection.

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Set<E>

Specified by:

iterator in class ImmutableCollection<E>

builder

public static <E> ImmutableSet.Builder<E> builder()

Returns a new builder. The generated builder is equivalent to the builder created by the ImmutableSet.Builder constructor.