set.java

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/*
 * @(#)Set.java	1.30 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program 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.   
 *   
 * This program 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 at /legal/license.txt).   
 *   
 * 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, CA 95054 or visit www.sun.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</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
 * @version 1.23, 02/02/00
 * @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 <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 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>.
     */
    Object[] toArray(Object 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 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