list.java

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/*
 * @(#)List.java	1.39 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;

/**
 * An ordered collection (also known as a <i>sequence</i>).  The user of this
 * interface has precise control over where in the list each element is
 * inserted.  The user can access elements by their integer index (position in
 * the list), and search for elements in the list.<p>
 *
 * Unlike sets, lists typically allow duplicate elements.  More formally,
 * lists typically allow pairs of elements <tt>e1</tt> and <tt>e2</tt>
 * such that <tt>e1.equals(e2)</tt>, and they typically allow multiple
 * null elements if they allow null elements at all.  It is not inconceivable
 * that someone might wish to implement a list that prohibits duplicates, by
 * throwing runtime exceptions when the user attempts to insert them, but we
 * expect this usage to be rare.<p>
 *
 * The <tt>List</tt> interface places additional stipulations, beyond those
 * specified in the <tt>Collection</tt> interface, on the contracts of the
 * <tt>iterator</tt>, <tt>add</tt>, <tt>remove</tt>, <tt>equals</tt>, and
 * <tt>hashCode</tt> methods.  Declarations for other inherited methods are
 * also included here for convenience.<p>
 *
 * The <tt>List</tt> interface provides four methods for positional (indexed)
 * access to list elements.  Lists (like Java arrays) are zero based.  Note
 * that these operations may execute in time proportional to the index value
 * for some implementations (the <tt>LinkedList</tt> class, for
 * example). Thus, iterating over the elements in a list is typically
 * preferable to indexing through it if the caller does not know the
 * implementation.<p>
 *
 * The <tt>List</tt> interface provides a special iterator, called a
 * <tt>ListIterator</tt>, that allows element insertion and replacement, and
 * bidirectional access in addition to the normal operations that the
 * <tt>Iterator</tt> interface provides.  A method is provided to obtain a
 * list iterator that starts at a specified position in the list.<p>
 *
 * The <tt>List</tt> interface provides two methods to search for a specified
 * object.  From a performance standpoint, these methods should be used with
 * caution.  In many implementations they will perform costly linear
 * searches.<p>
 *
 * The <tt>List</tt> interface provides two methods to efficiently insert and
 * remove multiple elements at an arbitrary point in the list.<p>
 *
 * Note: While it is permissible for lists to contain themselves as elements,
 * extreme caution is advised: the <tt>equals</tt> and <tt>hashCode</tt>
 * methods are no longer well defined on a such a list.
 *
 * <p>Some list 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 list 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 1.32, 02/02/00
 * @see Collection
 * @see Set
 * @see ArrayList
 * @see LinkedList
 * @see Vector
 * @see Arrays#asList(Object[])
 * @see Collections#nCopies(int, Object)
 * @see Collections#EMPTY_LIST
 * @see AbstractList
 * @see AbstractSequentialList
 * @since 1.2
 */

public interface List extends Collection {
    // Query Operations

    /**
     * Returns the number of elements in this list.  If this list contains
     * more than <tt>Integer.MAX_VALUE</tt> elements, returns
     * <tt>Integer.MAX_VALUE</tt>.
     *
     * @return the number of elements in this list.
     */
    int size();

    /**
     * Returns <tt>true</tt> if this list contains no elements.
     *
     * @return <tt>true</tt> if this list contains no elements.
     */
    boolean isEmpty();

    /**
     * 
     * Returns <tt>true</tt> if this list contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this list contains
     * at least one 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 list is to be tested.
     * @return <tt>true</tt> if this list contains the specified element.
     * @throws ClassCastException if the type of the specified element
     * 	       is incompatible with this list (optional).
     * @throws NullPointerException if the specified element is null and this
     *         list does not support null elements (optional).
     */
    boolean contains(Object o);

    /**
     * Returns an iterator over the elements in this list in proper sequence.
     *
     * @return an iterator over the elements in this list in proper sequence.
     */
    Iterator iterator();

    /**
     * Returns an array containing all of the elements in this list in proper
     * sequence.  Obeys the general contract of the
     * <tt>Collection.toArray</tt> method.
     *
     * @return an array containing all of the elements in this list in proper
     *	       sequence.
     * @see Arrays#asList(Object[])
     */
    Object[] toArray();

    /**
     * Returns an array containing all of the elements in this list in proper
     * sequence; 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 list 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 list.
     * 
     * @throws ArrayStoreException if the runtime type of the specified array
     * 		  is not a supertype of the runtime type of every element in
     * 		  this list.
     * @throws NullPointerException if the specified array is <tt>null</tt>.
     */
    Object[] toArray(Object a[]);


    // Modification Operations

    /**
     * Appends the specified element to the end of this list (optional
     * operation). <p>
     *
     * Lists that support this operation may place limitations on what
     * elements may be added to this list.  In particular, some
     * lists will refuse to add null elements, and others will impose
     * restrictions on the type of elements that may be added.  List
     * classes should clearly specify in their documentation any restrictions
     * on what elements may be added.
     *
     * @param o element to be appended to this list.
     * @return <tt>true</tt> (as per the general contract of the
     *            <tt>Collection.add</tt> method).
     * 
     * @throws UnsupportedOperationException if the <tt>add</tt> method is not
     * 		  supported by this list.
     * @throws ClassCastException if the class of the specified element
     * 		  prevents it from being added to this list.
     * @throws NullPointerException if the specified element is null and this
     *           list does not support null elements.
     * @throws IllegalArgumentException if some aspect of this element
     *            prevents it from being added to this list.
     */
    boolean add(Object o);

    /**
     * Removes the first occurrence in this list of the specified element 
     * (optional operation).  If this list does not contain the element, it is
     * unchanged.  More formally, removes the element with the lowest index i
     * such that <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> (if
     * such an element exists).
     *
     * @param o element to be removed from this list, if present.
     * @return <tt>true</tt> if this list contained the specified element.
     * @throws ClassCastException if the type of the specified element
     * 	          is incompatible with this list (optional).
     * @throws NullPointerException if the specified element is null and this
     *            list does not support null elements (optional).
     * @throws UnsupportedOperationException if the <tt>remove</tt> method is
     *		  not supported by this list.
     */
    boolean remove(Object o);


    // Bulk Modification Operations

    /**
     * 
     * Returns <tt>true</tt> if this list contains all of the elements of the
     * specified collection.
     *
     * @param  c collection to be checked for containment in this list.
     * @return <tt>true</tt> if this list 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
     *         list (optional).
     * @throws NullPointerException if the specified collection contains one
     *         or more null elements and this list does not support null
     *         elements (optional).
     * @throws NullPointerException if the specified collection is
     *         <tt>null</tt>.
     * @see #contains(Object)
     */
    boolean containsAll(Collection c);

    /**
     * Appends all of the elements in the specified collection to the end of
     * this list, in the order that they are returned by the specified
     * collection's iterator (optional operation).  The behavior of this
     * operation is unspecified if the specified collection is modified while
     * the operation is in progress.  (Note that this will occur if the
     * specified collection is this list, and it's nonempty.)
     *
     * @param c collection whose elements are to be added to this list.
     * @return <tt>true</tt> if this list changed as a result of the call.
     * 
     * @throws UnsupportedOperationException if the <tt>addAll</tt> method is
     *         not supported by this list.
     * @throws ClassCastException if the class of an element in the specified
     * 	       collection prevents it from being added to this list.
     * @throws NullPointerException if the specified collection contains one
     *         or more null elements and this list does not support null
     *         elements, or if the specified collection is <tt>null</tt>.
     * @throws IllegalArgumentException if some aspect of an element in the
     *         specified collection prevents it from being added to this
     *         list.
     * @see #add(Object)
     */
    boolean addAll(Collection c);

    /**
     * Inserts all of the elements in the specified collection into this
     * list at the specified position (optional operation).  Shifts the
     * element currently at that position (if any) and any subsequent
     * elements to the right (increases their indices).  The new elements
     * will appear in this list in the order that they are returned by the
     * specified collection's iterator.  The behavior of this operation is
     * unspecified if the specified collection is modified while the
     * operation is in progress.  (Note that this will occur if the specified
     * collection is this list, and it's nonempty.)
     *
     * @param index index at which to insert first element from the specified
     *	            collection.
     * @param c elements to be inserted into this list.
     * @return <tt>true</tt> if this list changed as a result of the call.
     * 
     * @throws UnsupportedOperationException if the <tt>addAll</tt> method is
     *		  not supported by this list.