/* * Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ 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 set abstraction. * *

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.) * *

The additional stipulation on constructors is, not surprisingly, * that all constructors must create a set that contains no duplicate elements * (as defined above). * *

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. * *

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. * *

Unmodifiable Sets

*

The {@link Set#of(Object...) Set.of} and * {@link Set#copyOf Set.copyOf} static factory methods * provide a convenient way to create unmodifiable sets. The {@code Set} * instances created by these methods have the following characteristics: * *

* *

This interface is a member of the * * Java Collections Framework. * * @param 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 extends Collection { // 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 * (optional) * @throws NullPointerException if the specified element is null and this * set does not permit null elements * (optional) */ 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 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. * *

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. * *

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. * *

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 only if the caller knows that this set does not contain * any null elements.) * *

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. * *

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. * *

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}: * * 

     *     String[] y = x.toArray(new String[0]);
* * 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[] 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. * *

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 * (optional) * @throws NullPointerException if the specified element is null and this * set does not permit null elements * (optional) * @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 subset 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 * (optional) * @throws NullPointerException if the specified collection contains one * or more null elements and this set does not permit null * elements * (optional), * 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 union 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 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 * intersection 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 * (optional) * @throws NullPointerException if this set contains a null element and the * specified collection does not permit null elements * (optional), * 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 asymmetric set difference 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 * (optional) * @throws NullPointerException if this set contains a null element and the * specified collection does not permit null elements * (optional), * 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. * *

The {@code Spliterator} reports {@link Spliterator#DISTINCT}. * Implementations should document the reporting of additional * characteristic values. * * @implSpec * The default implementation creates a * late-binding spliterator * from the set's {@code Iterator}. The spliterator inherits the * fail-fast properties of the set's iterator. *

* 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 spliterator() { return Spliterators.spliterator(this, Spliterator.DISTINCT); } /** * Returns an unmodifiable set containing zero elements. * See Unmodifiable Sets for details. * * @param the {@code Set}'s element type * @return an empty {@code Set} * * @since 9 */ @SuppressWarnings("unchecked") static Set of() { return (Set) ImmutableCollections.EMPTY_SET; } /** * Returns an unmodifiable set containing one element. * See Unmodifiable Sets for details. * * @param 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 Set of(E e1) { return new ImmutableCollections.Set12<>(e1); } /** * Returns an unmodifiable set containing two elements. * See Unmodifiable Sets for details. * * @param 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 Set of(E e1, E e2) { return new ImmutableCollections.Set12<>(e1, e2); } /** * Returns an unmodifiable set containing three elements. * See Unmodifiable Sets for details. * * @param 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 Set of(E e1, E e2, E e3) { return new ImmutableCollections.SetN<>(e1, e2, e3); } /** * Returns an unmodifiable set containing four elements. * See Unmodifiable Sets for details. * * @param 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 Set of(E e1, E e2, E e3, E e4) { return new ImmutableCollections.SetN<>(e1, e2, e3, e4); } /** * Returns an unmodifiable set containing five elements. * See Unmodifiable Sets for details. * * @param 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 Set of(E e1, E e2, E e3, E e4, E e5) { return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5); } /** * Returns an unmodifiable set containing six elements. * See Unmodifiable Sets for details. * * @param 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 Set 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 unmodifiable set containing seven elements. * See Unmodifiable Sets for details. * * @param 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 Set 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 unmodifiable set containing eight elements. * See Unmodifiable Sets for details. * * @param 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 Set 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 unmodifiable set containing nine elements. * See Unmodifiable Sets for details. * * @param 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 Set 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 unmodifiable set containing ten elements. * See Unmodifiable Sets for details. * * @param 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 Set 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 unmodifiable set containing an arbitrary number of elements. * See Unmodifiable Sets 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: * * 

{@code
     *     String[] array = ... ;
     *     Set list = Set.of(array);
     * }
* * This will cause the {@link Set#of(Object) Set.of(E)} method * to be invoked instead. * * @param 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 Set of(E... elements) { switch (elements.length) { // implicit null check of elements case 0: @SuppressWarnings("unchecked") var set = (Set) ImmutableCollections.EMPTY_SET; return set; case 1: return new ImmutableCollections.Set12<>(elements[0]); case 2: return new ImmutableCollections.Set12<>(elements[0], elements[1]); default: return new ImmutableCollections.SetN<>(elements); } } /** * Returns an unmodifiable Set containing the elements * of the given Collection. The given Collection must not be null, and it must not * contain any null elements. If the given Collection contains duplicate elements, * an arbitrary element of the duplicates is preserved. If the given Collection is * subsequently modified, the returned Set will not reflect such modifications. * * @implNote * If the given Collection is an unmodifiable Set, * calling copyOf will generally not create a copy. * * @param the {@code Set}'s element type * @param coll a {@code Collection} from which elements are drawn, must be non-null * @return a {@code Set} containing the elements of the given {@code Collection} * @throws NullPointerException if coll is null, or if it contains any nulls * @since 10 */ @SuppressWarnings("unchecked") static Set copyOf(Collection coll) { if (coll instanceof ImmutableCollections.AbstractImmutableSet) { return (Set)coll; } else { return (Set)Set.of(new HashSet<>(coll).toArray()); } } }