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
See Also:
ImmutableList, ImmutableMap, Serialized Form

Method Summary
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()
           
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.
 String toString()
           
 
Methods inherited from class com.google.common.collect.ImmutableCollection
add, addAll, clear, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray
 
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, iterator, 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... 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).

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, 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(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

toString

public String toString()
Overrides:
toString in class ImmutableCollection<E>