/*

 * Copyright 1997-2006 Sun Microsystems, Inc.  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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

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 */

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

 * @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&nbsp;?&nbsp;e==null&nbsp;:&nbsp;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&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;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&nbsp;?&nbsp;e==null&nbsp;:&nbsp;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();

}