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/* * @(#)Set.java 1.39 06/04/21 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util; /** * A collection that contains no duplicate elements. More formally, sets * contain no pair of elements <code>e1</code> and <code>e2</code> such that * <code>e1.equals(e2)</code>, and at most one null element. As implied by * its name, this interface models the mathematical <i>set</i> abstraction. * * <p>The <tt>Set</tt> interface places additional stipulations, beyond those * inherited from the <tt>Collection</tt> interface, on the contracts of all * constructors and on the contracts of the <tt>add</tt>, <tt>equals</tt> and * <tt>hashCode</tt> methods. Declarations for other inherited methods are * also included here for convenience. (The specifications accompanying these * declarations have been tailored to the <tt>Set</tt> 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 <tt>equals</tt> 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 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. 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. * * <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 * @version 1.39, 04/21/06 * @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 <tt>Integer.MAX_VALUE</tt> elements, returns * <tt>Integer.MAX_VALUE</tt>. * * @return the number of elements in this set (its cardinality) */ int size(); /** * Returns <tt>true</tt> if this set contains no elements. * * @return <tt>true</tt> if this set contains no elements */ boolean isEmpty(); /** * Returns <tt>true</tt> if this set contains the specified element. * More formally, returns <tt>true</tt> if and only if this set * contains an element <tt>e</tt> such that * <tt>(o==null ? e==null : o.equals(e))</tt>. * * @param o element whose presence in this set is to be tested * @return <tt>true</tt> 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<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 * <tt>null</tt>. (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 <tt>x</tt> is a set known to contain only strings. * The following code can be used to dump the set into a newly allocated * array of <tt>String</tt>: * * <pre> * String[] y = x.toArray(new String[0]);</pre> * * Note that <tt>toArray(new Object[0])</tt> is identical in function to * <tt>toArray()</tt>. * * @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 * <tt>e</tt> to this set if the set contains no element <tt>e2</tt> * such that * <tt>(e==null ? e2==null : e.equals(e2))</tt>. * If this set already contains the element, the call leaves the set * unchanged and returns <tt>false</tt>. 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 * <tt>null</tt>, 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 <tt>true</tt> if this set did not already contain the specified * element * @throws UnsupportedOperationException if the <tt>add</tt> 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 <tt>e</tt> * such that * <tt>(o==null ? e==null : o.equals(e))</tt>, if * this set contains such an element. Returns <tt>true</tt> 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 <tt>true</tt> 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 <tt>remove</tt> operation * is not supported by this set */ boolean remove(Object o); // Bulk Operations /** * Returns <tt>true</tt> if this set contains all of the elements of the * specified collection. If the specified collection is also a set, this * method returns <tt>true</tt> if it is a <i>subset</i> of this set. * * @param c collection to be checked for containment in this set * @return <tt>true</tt> 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 <tt>addAll</tt> 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 <tt>true</tt> if this set changed as a result of the call * * @throws UnsupportedOperationException if the <tt>addAll</tt> 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 <tt>true</tt> if this set changed as a result of the call * @throws UnsupportedOperationException if the <tt>retainAll</tt> 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 <i>asymmetric set difference</i> of * the two sets. * * @param c collection containing elements to be removed from this set * @return <tt>true</tt> if this set changed as a result of the call * @throws UnsupportedOperationException if the <tt>removeAll</tt> 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 <tt>clear</tt> method * is not supported by this set */ void clear(); // Comparison and hashing /** * Compares the specified object with this set for equality. Returns * <tt>true</tt> 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 <tt>true</tt> 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 <tt>null</tt> element is defined to be zero. * This ensures that <tt>s1.equals(s2)</tt> implies that * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt> * and <tt>s2</tt>, 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(); }
