/* * @(#)Set.java 1.35 04/02/19 * * Copyright 2004 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 e1 and e2 such that * e1.equals(e2), and at most one null element. As implied by * its name, this interface models the mathematical set abstraction.

* * The Set interface places additional stipulations, beyond those * inherited from the Collection interface, on the contracts of all * constructors and on the contracts of the add, equals and * hashCode methods. Declarations for other inherited methods are * also included here for convenience. (The specifications accompanying these * declarations have been tailored to the 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 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 * NullPointerException or 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. * *

This interface is a member of the * * Java Collections Framework. * * @author Josh Bloch * @author Neal Gafter * @version 1.35, 02/19/04 * @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 Integer.MAX_VALUE elements, returns * Integer.MAX_VALUE. * * @return the number of elements in this set (its cardinality). */ int size(); /** * Returns true if this set contains no elements. * * @return true if this set contains no elements. */ boolean isEmpty(); /** * Returns true if this set contains the specified element. More * formally, returns true if and only if this set contains an * element e such that (o==null ? e==null : * o.equals(e)). * * @param o element whose presence in this set is to be tested. * @return 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 support 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. * Obeys the general contract of the Collection.toArray method. * * @return an array containing all of 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. * Obeys the general contract of the * Collection.toArray(Object[]) method. * * @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 the elements of this set. * @throws ArrayStoreException the runtime type of a 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, * o, to this set if this set contains no element * e such that (o==null ? e==null : * o.equals(e)). If this set already contains the specified * element, the call leaves this set unchanged and returns 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 * null, and throwing an exception, as described in the * specification for Collection.add. Individual set * implementations should clearly document any restrictions on the * elements that they may contain. * * @param o element to be added to this set. * @return true if this set did not already contain the specified * element. * * @throws UnsupportedOperationException if the add method 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 support null elements. * @throws IllegalArgumentException if some aspect of the specified element * prevents it from being added to this set. */ boolean add(E o); /** * Removes the specified element from this set if it is present (optional * operation). More formally, removes an element e such that * (o==null ? e==null : o.equals(e)), if the set contains * such an element. Returns true if the set contained the * specified element (or equivalently, if the set changed as a result of * the call). (The set will not contain the specified element once the * call returns.) * * @param o object to be removed from this set, if present. * @return true if the 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 support null elements (optional). * @throws UnsupportedOperationException if the remove method is * not supported by this set. */ boolean remove(Object o); // Bulk Operations /** * Returns true if this set contains all of the elements of the * specified collection. If the specified collection is also a set, this * method returns true if it is a subset of this set. * * @param c collection to be checked for containment in this set. * @return 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 support null * elements (optional). * @throws NullPointerException 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 addAll operation effectively * modifies this set so that its value is the union of the two * sets. The behavior of this operation is unspecified if the specified * collection is modified while the operation is in progress. * * @param c collection whose elements are to be added to this set. * @return true if this set changed as a result of the call. * * @throws UnsupportedOperationException if the addAll method is * not supported by this set. * @throws ClassCastException if the class of some 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 support null * elements, or if the specified collection is null. * @throws IllegalArgumentException if some aspect of some 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 that defines which elements this set will retain. * @return true if this collection changed as a result of the * call. * @throws UnsupportedOperationException if the retainAll method * is not supported by this Collection. * @throws ClassCastException if the types of one or more elements in this * set are incompatible with the specified collection * (optional). * @throws NullPointerException if this set contains a null element and * the specified collection does not support null elements * (optional). * @throws NullPointerException 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 that defines which elements will be removed from * this set. * @return true if this set changed as a result of the call. * * @throws UnsupportedOperationException if the removeAll * method is not supported by this Collection. * @throws ClassCastException if the types of one or more elements in this * set are incompatible with the specified collection * (optional). * @throws NullPointerException if this set contains a null element and * the specified collection does not support null elements * (optional). * @throws NullPointerException if the specified collection is * null. * @see #remove(Object) */ boolean removeAll(Collection c); /** * Removes all of the elements from this set (optional operation). * This set will be empty after this call returns (unless it throws an * exception). * * @throws UnsupportedOperationException if the clear method * is not supported by this set. */ void clear(); // Comparison and hashing /** * Compares the specified object with this set for equality. Returns * 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 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 hashcode of a null element is defined to be zero. * This ensures that s1.equals(s2) implies that * s1.hashCode()==s2.hashCode() for any two sets * s1 and s2, as required by the general * contract of the Object.hashCode method. * * @return the hash code value for this set. * @see Object#hashCode() * @see Object#equals(Object) * @see Set#equals(Object) */ int hashCode(); }