com.google.common.collect
Class ImmutableSet<E>

java.lang.Object
  extended by com.google.common.collect.ImmutableCollection<E>
      extended by com.google.common.collect.ImmutableSet<E>
All Implemented Interfaces:
Serializable, Iterable<E>, Collection<E>, Set<E>
Direct Known Subclasses:
ImmutableSortedSet

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), 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.

Author:
Kevin Bourrillion, Nick Kralevich
See Also:
ImmutableList, ImmutableMap, Serialized Form

Nested Class Summary
static class ImmutableSet.Builder<E>
          A builder for creating immutable set instances, especially public static final sets ("constant sets").
 
Method Summary
static
<E> ImmutableSet.Builder<E>
builder()
          Returns a new builder.
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)
          Indicates whether some other object is "equal to" this one.
 int hashCode()
          Returns a hash code value for the object.
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... elements)
          Returns an immutable set containing the given elements, in order.
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.
 
Methods inherited from class com.google.common.collect.ImmutableCollection
add, addAll, 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... 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 (but too many of these may result in the set being sized inappropriately).

Throws:
NullPointerException - if any of elements is null

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 (but too many of these may result in the set being sized inappropriately). 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, if elements is an ImmutableSet (but not an ImmutableSortedSet), no copy will actually be performed, and the given set itself will be returned.

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

equals

public boolean equals(@Nullable
                      Object object)
Description copied from class: java.lang.Object
Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

Specified by:
equals in interface Collection<E>
Specified by:
equals in interface Set<E>
Overrides:
equals in class Object
Parameters:
object - the reference object with which to compare.
Returns:
true if this object is the same as the obj argument; false otherwise.
See Also:
Object.hashCode(), Hashtable

hashCode

public int hashCode()
Description copied from class: java.lang.Object
Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode is:

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Specified by:
hashCode in interface Collection<E>
Specified by:
hashCode in interface Set<E>
Overrides:
hashCode in class Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

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>
Returns:
an Iterator over the elements in this collection

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.