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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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package java.util;
/**
* A collection that contains no duplicate elements. More formally, sets
* contain no pair of elements {@code e1} and {@code e2} such that
* {@code e1.equals(e2)}, and at most one null element. As implied by
* its name, this interface models the mathematical <i>set</i> abstraction.
*
* <p>The {@code Set} interface places additional stipulations, beyond those
* inherited from the {@code Collection} interface, on the contracts of all
* constructors and on the contracts of the {@code add}, {@code equals} and
* {@code hashCode} methods. Declarations for other inherited methods are
* also included here for convenience. (The specifications accompanying these
* declarations have been tailored to the {@code Set} interface, but they do
* not contain any additional stipulations.)
*
* <p>The additional stipulation on constructors is, not surprisingly,
* that all constructors must create a set that contains no duplicate elements
* (as defined above).
*
* <p>Note: Great care must be exercised if mutable objects are used as set
* elements. The behavior of a set is not specified if the value of an object
* is changed in a manner that affects {@code equals} comparisons while the
* object is an element in the set. A special case of this prohibition is
* that it is not permissible for a set to contain itself as an element.
*
* <p>Some set implementations have restrictions on the elements that
* they may contain. For example, some implementations prohibit null elements,
* and some have restrictions on the types of their elements. Attempting to
* add an ineligible element throws an unchecked exception, typically
* {@code NullPointerException} or {@code ClassCastException}. Attempting
* to query the presence of an ineligible element may throw an exception,
* or it may simply return false; some implementations will exhibit the former
* behavior and some will exhibit the latter. More generally, attempting an
* operation on an ineligible element whose completion would not result in
* the insertion of an ineligible element into the set may throw an
* exception or it may succeed, at the option of the implementation.
* Such exceptions are marked as "optional" in the specification for this
* interface.
*
* <h2><a name="immutable">Immutable Set Static Factory Methods</a></h2>
* <p>The {@link Set#of(Object...) Set.of()} static factory methods
* provide a convenient way to create immutable sets. The {@code Set}
* instances created by these methods have the following characteristics:
*
* <ul>
* <li>They are <em>structurally immutable</em>. Elements cannot be added or
* removed. Calling any mutator method will always cause
* {@code UnsupportedOperationException} to be thrown.
* However, if the contained elements are themselves mutable, this may cause the
* Set to behave inconsistently or its contents to appear to change.
* <li>They disallow {@code null} elements. Attempts to create them with
* {@code null} elements result in {@code NullPointerException}.
* <li>They are serializable if all elements are serializable.
* <li>They reject duplicate elements at creation time. Duplicate elements
* passed to a static factory method result in {@code IllegalArgumentException}.
* <li>The iteration order of set elements is unspecified and is subject to change.
* <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>.
* Callers should make no assumptions about the identity of the returned instances.
* Factories are free to create new instances or reuse existing ones. Therefore,
* identity-sensitive operations on these instances (reference equality ({@code ==}),
* identity hash code, and synchronization) are unreliable and should be avoided.
* <li>They are serialized as specified on the
* <a href="{@docRoot}/serialized-form.html#java.util.CollSer">Serialized Form</a>
* page.
* </ul>
*
* <p>This interface is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @param <E> the type of elements maintained by this set
*
* @author Josh Bloch
* @author Neal Gafter
* @see Collection
* @see List
* @see SortedSet
* @see HashSet
* @see TreeSet
* @see AbstractSet
* @see Collections#singleton(java.lang.Object)
* @see Collections#EMPTY_SET
* @since 1.2
*/
public interface Set<E> extends Collection<E> {
// Query Operations
/**
* Returns the number of elements in this set (its cardinality). If this
* set contains more than {@code Integer.MAX_VALUE} elements, returns
* {@code Integer.MAX_VALUE}.
*
* @return the number of elements in this set (its cardinality)
*/
int size();
/**
* Returns {@code true} if this set contains no elements.
*
* @return {@code true} if this set contains no elements
*/
boolean isEmpty();
/**
* Returns {@code true} if this set contains the specified element.
* More formally, returns {@code true} if and only if this set
* contains an element {@code e} such that
* {@code Objects.equals(o, e)}.
*
* @param o element whose presence in this set is to be tested
* @return {@code true} if this set contains the specified element
* @throws ClassCastException if the type of the specified element
* is incompatible with this set
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified element is null and this
* set does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>)
*/
boolean contains(Object o);
/**
* Returns an iterator over the elements in this set. The elements are
* returned in no particular order (unless this set is an instance of some
* class that provides a guarantee).
*
* @return an iterator over the elements in this set
*/
Iterator<E> iterator();
/**
* Returns an array containing all of the elements in this set.
* If this set makes any guarantees as to what order its elements
* are returned by its iterator, this method must return the
* elements in the same order.
*
* <p>The returned array will be "safe" in that no references to it
* are maintained by this set. (In other words, this method must
* allocate a new array even if this set is backed by an array).
* The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all the elements in this set
*/
Object[] toArray();
/**
* Returns an array containing all of the elements in this set; the
* runtime type of the returned array is that of the specified array.
* If the set fits in the specified array, it is returned therein.
* Otherwise, a new array is allocated with the runtime type of the
* specified array and the size of this set.
*
* <p>If this set fits in the specified array with room to spare
* (i.e., the array has more elements than this set), the element in
* the array immediately following the end of the set is set to
* {@code null}. (This is useful in determining the length of this
* set <i>only</i> if the caller knows that this set does not contain
* any null elements.)
*
* <p>If this set makes any guarantees as to what order its elements
* are returned by its iterator, this method must return the elements
* in the same order.
*
* <p>Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
* <p>Suppose {@code x} is a set known to contain only strings.
* The following code can be used to dump the set into a newly allocated
* array of {@code String}:
*
* <pre>
* String[] y = x.toArray(new String[0]);</pre>
*
* Note that {@code toArray(new Object[0])} is identical in function to
* {@code toArray()}.
*
* @param a the array into which the elements of this set are to be
* stored, if it is big enough; otherwise, a new array of the same
* runtime type is allocated for this purpose.
* @return an array containing all the elements in this set
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in this
* set
* @throws NullPointerException if the specified array is null
*/
<T> T[] toArray(T[] a);
// Modification Operations
/**
* Adds the specified element to this set if it is not already present
* (optional operation). More formally, adds the specified element
* {@code e} to this set if the set contains no element {@code e2}
* such that
* {@code Objects.equals(e, e2)}.
* If this set already contains the element, the call leaves the set
* unchanged and returns {@code false}. In combination with the
* restriction on constructors, this ensures that sets never contain
* duplicate elements.
*
* <p>The stipulation above does not imply that sets must accept all
* elements; sets may refuse to add any particular element, including
* {@code null}, and throw an exception, as described in the
* specification for {@link Collection#add Collection.add}.
* Individual set implementations should clearly document any
* restrictions on the elements that they may contain.
*
* @param e element to be added to this set
* @return {@code true} if this set did not already contain the specified
* element
* @throws UnsupportedOperationException if the {@code add} operation
* is not supported by this set
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this set
* @throws NullPointerException if the specified element is null and this
* set does not permit null elements
* @throws IllegalArgumentException if some property of the specified element
* prevents it from being added to this set
*/
boolean add(E e);
/**
* Removes the specified element from this set if it is present
* (optional operation). More formally, removes an element {@code e}
* such that
* {@code Objects.equals(o, e)}, if
* this set contains such an element. Returns {@code true} if this set
* contained the element (or equivalently, if this set changed as a
* result of the call). (This set will not contain the element once the
* call returns.)
*
* @param o object to be removed from this set, if present
* @return {@code true} if this set contained the specified element
* @throws ClassCastException if the type of the specified element
* is incompatible with this set
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified element is null and this
* set does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws UnsupportedOperationException if the {@code remove} operation
* is not supported by this set
*/
boolean remove(Object o);
// Bulk Operations
/**
* Returns {@code true} if this set contains all of the elements of the
* specified collection. If the specified collection is also a set, this
* method returns {@code true} if it is a <i>subset</i> of this set.
*
* @param c collection to be checked for containment in this set
* @return {@code true} if this set contains all of the elements of the
* specified collection
* @throws ClassCastException if the types of one or more elements
* in the specified collection are incompatible with this
* set
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified collection contains one
* or more null elements and this set does not permit null
* elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see #contains(Object)
*/
boolean containsAll(Collection<?> c);
/**
* Adds all of the elements in the specified collection to this set if
* they're not already present (optional operation). If the specified
* collection is also a set, the {@code addAll} operation effectively
* modifies this set so that its value is the <i>union</i> of the two
* sets. The behavior of this operation is undefined if the specified
* collection is modified while the operation is in progress.
*
* @param c collection containing elements to be added to this set
* @return {@code true} if this set changed as a result of the call
*
* @throws UnsupportedOperationException if the {@code addAll} operation
* is not supported by this set
* @throws ClassCastException if the class of an element of the
* specified collection prevents it from being added to this set
* @throws NullPointerException if the specified collection contains one
* or more null elements and this set does not permit null
* elements, or if the specified collection is null
* @throws IllegalArgumentException if some property of an element of the
* specified collection prevents it from being added to this set
* @see #add(Object)
*/
boolean addAll(Collection<? extends E> c);
/**
* Retains only the elements in this set that are contained in the
* specified collection (optional operation). In other words, removes
* from this set all of its elements that are not contained in the
* specified collection. If the specified collection is also a set, this
* operation effectively modifies this set so that its value is the
* <i>intersection</i> of the two sets.
*
* @param c collection containing elements to be retained in this set
* @return {@code true} if this set changed as a result of the call
* @throws UnsupportedOperationException if the {@code retainAll} operation
* is not supported by this set
* @throws ClassCastException if the class of an element of this set
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this set contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see #remove(Object)
*/
boolean retainAll(Collection<?> c);
/**
* Removes from this set all of its elements that are contained in the
* specified collection (optional operation). If the specified
* collection is also a set, this operation effectively modifies this
* set so that its value is the <i>asymmetric set difference</i> of
* the two sets.
*
* @param c collection containing elements to be removed from this set
* @return {@code true} if this set changed as a result of the call
* @throws UnsupportedOperationException if the {@code removeAll} operation
* is not supported by this set
* @throws ClassCastException if the class of an element of this set
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this set contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see #remove(Object)
* @see #contains(Object)
*/
boolean removeAll(Collection<?> c);
/**
* Removes all of the elements from this set (optional operation).
* The set will be empty after this call returns.
*
* @throws UnsupportedOperationException if the {@code clear} method
* is not supported by this set
*/
void clear();
// Comparison and hashing
/**
* Compares the specified object with this set for equality. Returns
* {@code true} if the specified object is also a set, the two sets
* have the same size, and every member of the specified set is
* contained in this set (or equivalently, every member of this set is
* contained in the specified set). This definition ensures that the
* equals method works properly across different implementations of the
* set interface.
*
* @param o object to be compared for equality with this set
* @return {@code true} if the specified object is equal to this set
*/
boolean equals(Object o);
/**
* Returns the hash code value for this set. The hash code of a set is
* defined to be the sum of the hash codes of the elements in the set,
* where the hash code of a {@code null} element is defined to be zero.
* This ensures that {@code s1.equals(s2)} implies that
* {@code s1.hashCode()==s2.hashCode()} for any two sets {@code s1}
* and {@code s2}, as required by the general contract of
* {@link Object#hashCode}.
*
* @return the hash code value for this set
* @see Object#equals(Object)
* @see Set#equals(Object)
*/
int hashCode();
/**
* Creates a {@code Spliterator} over the elements in this set.
*
* <p>The {@code Spliterator} reports {@link Spliterator#DISTINCT}.
* Implementations should document the reporting of additional
* characteristic values.
*
* @implSpec
* The default implementation creates a
* <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
* from the set's {@code Iterator}. The spliterator inherits the
* <em>fail-fast</em> properties of the set's iterator.
* <p>
* The created {@code Spliterator} additionally reports
* {@link Spliterator#SIZED}.
*
* @implNote
* The created {@code Spliterator} additionally reports
* {@link Spliterator#SUBSIZED}.
*
* @return a {@code Spliterator} over the elements in this set
* @since 1.8
*/
@Override
default Spliterator<E> spliterator() {
return Spliterators.spliterator(this, Spliterator.DISTINCT);
}
/**
* Returns an immutable set containing zero elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @return an empty {@code Set}
*
* @since 9
*/
static <E> Set<E> of() {
return ImmutableCollections.Set0.instance();
}
/**
* Returns an immutable set containing one element.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the single element
* @return a {@code Set} containing the specified element
* @throws NullPointerException if the element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1) {
return new ImmutableCollections.Set1<>(e1);
}
/**
* Returns an immutable set containing two elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if the elements are duplicates
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2) {
return new ImmutableCollections.Set2<>(e1, e2);
}
/**
* Returns an immutable set containing three elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3) {
return new ImmutableCollections.SetN<>(e1, e2, e3);
}
/**
* Returns an immutable set containing four elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @param e4 the fourth element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3, E e4) {
return new ImmutableCollections.SetN<>(e1, e2, e3, e4);
}
/**
* Returns an immutable set containing five elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @param e4 the fourth element
* @param e5 the fifth element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5) {
return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5);
}
/**
* Returns an immutable set containing six elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @param e4 the fourth element
* @param e5 the fifth element
* @param e6 the sixth element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
e6);
}
/**
* Returns an immutable set containing seven elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @param e4 the fourth element
* @param e5 the fifth element
* @param e6 the sixth element
* @param e7 the seventh element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
e6, e7);
}
/**
* Returns an immutable set containing eight elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @param e4 the fourth element
* @param e5 the fifth element
* @param e6 the sixth element
* @param e7 the seventh element
* @param e8 the eighth element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
e6, e7, e8);
}
/**
* Returns an immutable set containing nine elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @param e4 the fourth element
* @param e5 the fifth element
* @param e6 the sixth element
* @param e7 the seventh element
* @param e8 the eighth element
* @param e9 the ninth element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
e6, e7, e8, e9);
}
/**
* Returns an immutable set containing ten elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @param <E> the {@code Set}'s element type
* @param e1 the first element
* @param e2 the second element
* @param e3 the third element
* @param e4 the fourth element
* @param e5 the fifth element
* @param e6 the sixth element
* @param e7 the seventh element
* @param e8 the eighth element
* @param e9 the ninth element
* @param e10 the tenth element
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null}
*
* @since 9
*/
static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
e6, e7, e8, e9, e10);
}
/**
* Returns an immutable set containing an arbitrary number of elements.
* See <a href="#immutable">Immutable Set Static Factory Methods</a> for details.
*
* @apiNote
* This method also accepts a single array as an argument. The element type of
* the resulting set will be the component type of the array, and the size of
* the set will be equal to the length of the array. To create a set with
* a single element that is an array, do the following:
*
* <pre>{@code
* String[] array = ... ;
* Set<String[]> list = Set.<String[]>of(array);
* }</pre>
*
* This will cause the {@link Set#of(Object) Set.of(E)} method
* to be invoked instead.
*
* @param <E> the {@code Set}'s element type
* @param elements the elements to be contained in the set
* @return a {@code Set} containing the specified elements
* @throws IllegalArgumentException if there are any duplicate elements
* @throws NullPointerException if an element is {@code null} or if the array is {@code null}
*
* @since 9
*/
@SafeVarargs
@SuppressWarnings("varargs")
static <E> Set<E> of(E... elements) {
Objects.requireNonNull(elements);
switch (elements.length) {
case 0:
return ImmutableCollections.Set0.instance();
case 1:
return new ImmutableCollections.Set1<>(elements[0]);
case 2:
return new ImmutableCollections.Set2<>(elements[0], elements[1]);
default:
return new ImmutableCollections.SetN<>(elements);
}
}
}