/*
* @(#)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 <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 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
* <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}/../guide/collections/index.html">
* Java Collections Framework</a>.
*
* @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<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 <code>e</code> such that <code>(o==null ? e==null :
* o.equals(e))</code>.
*
* @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 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<E> iterator();
/**
* Returns an array containing all of the elements in this set.
* Obeys the general contract of the <tt>Collection.toArray</tt> 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
* <tt>Collection.toArray(Object[])</tt> 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 <tt>null</tt>.
*/
<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>o</code>, to this set if this set contains no element
* <code>e</code> such that <code>(o==null ? e==null :
* o.equals(e))</code>. If this set already contains the specified
* element, the call leaves this 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 throwing an exception, as described in the
* specification for <tt>Collection.add</tt>. 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 <tt>true</tt> if this set did not already contain the specified
* element.
*
* @throws UnsupportedOperationException if the <tt>add</tt> 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 <code>e</code> such that
* <code>(o==null ? e==null : o.equals(e))</code>, if the set contains
* such an element. Returns <tt>true</tt> 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 <tt>remove</tt> method 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 support null
* elements (optional).
* @throws NullPointerException if the specified collection is
* <tt>null</tt>.
* @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 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 <tt>true</tt> if this set changed as a result of the call.
*
* @throws UnsupportedOperationException if the <tt>addAll</tt> 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 <tt>null</tt>.
* @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<? 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 that defines which elements this set will retain.
* @return <tt>true</tt> if this collection changed as a result of the
* call.
* @throws UnsupportedOperationException if the <tt>retainAll</tt> 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
* <tt>null</tt>.
* @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 that defines which elements will 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>
* 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
* <tt>null</tt>.
* @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 <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 hashcode of a <tt>null</tt> element is defined to be zero.
* This ensures that <code>s1.equals(s2)</code> implies that
* <code>s1.hashCode()==s2.hashCode()</code> for any two sets
* <code>s1</code> and <code>s2</code>, as required by the general
* contract of the <tt>Object.hashCode</tt> method.
*
* @return the hash code value for this set.
* @see Object#hashCode()
* @see Object#equals(Object)
* @see Set#equals(Object)
*/
int hashCode();
}
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