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 * 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,

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 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

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 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}/../technotes/guides/collections/index.html">

 * Java Collections Framework</a>.

 *

 * @param <E> the type of elements in this list

 *

 * @author  Josh Bloch

 * @author  Neal Gafter

 * @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<E> extends Collection<E> {

    // 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

     * (<a href="Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if the specified element is null and this

     *         list does not permit null elements

     * (<a href="Collection.html#optional-restrictions">optional</a>)

     */

    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<E> iterator();

    /**

     * Returns an array containing all of the elements in this list in proper

     * sequence (from first to last element).

     *

     * <p>The returned array will be "safe" in that no references to it are

     * maintained by this list.  (In other words, this method must

     * allocate a new array even if this list 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 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 (from first to last element); the runtime type of

     * the returned array is that of the specified array.  If the list 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 list.

     *

     * <p>If the list fits in the specified array with room to spare (i.e.,

     * the array has more elements than the list), the element in the array

     * immediately following the end of the list is set to <tt>null</tt>.

     * (This is useful in determining the length of the list <i>only</i> if

     * the caller knows that the list does not contain any null elements.)

     *

     * <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 list known to contain only strings.

     * The following code can be used to dump the list 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 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 null

     */

    <T> T[] toArray(T[] 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 e element to be appended to this list

     * @return <tt>true</tt> (as specified by {@link Collection#add})

     * @throws UnsupportedOperationException if the <tt>add</tt> operation

     *         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 permit null elements

     * @throws IllegalArgumentException if some property of this element

     *         prevents it from being added to this list

     */

    boolean add(E e);

    /**

     * Removes the first occurrence of the specified element from this list,

     * if it is present (optional operation).  If this list does not contain

     * the element, it is unchanged.  More formally, removes the element with

     * the lowest index <tt>i</tt> such that

     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>

     * (if such an element exists).  Returns <tt>true</tt> if this list

     * contained the specified element (or equivalently, if this list changed

     * as a result of the call).

     *

     * @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

     * (<a href="Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if the specified element is null and this

     *         list does not permit null elements

     * (<a href="Collection.html#optional-restrictions">optional</a>)

     * @throws UnsupportedOperationException if the <tt>remove</tt> operation

     *         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

     * (<a href="Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if the specified collection contains one

     *         or more null elements and this list does not permit null

     *         elements

     *         (<a href="Collection.html#optional-restrictions">optional</a>),

     *         or if the specified collection is null

     * @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 undefined 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 containing elements 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> operation

     *         is not supported by this list

     * @throws ClassCastException if the class of an element of 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 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 list

     * @see #add(Object)

     */

    boolean addAll(Collection<? extends E> 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

     * undefined 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 the first element from the

     *              specified collection

     * @param c collection containing elements 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> operation

     *         is not supported by this list

     * @throws ClassCastException if the class of an element of 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 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 list

     * @throws IndexOutOfBoundsException if the index is out of range

     *         (<tt>index &lt; 0 || index &gt; size()</tt>)

     */

    boolean addAll(int index, Collection<? extends E> c);

    /**

     * Removes from this list all of its elements that are contained in the

     * specified collection (optional operation).

     *

     * @param c collection containing elements to be removed from this list

     * @return <tt>true</tt> if this list changed as a result of the call

     * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation

     *         is not supported by this list

     * @throws ClassCastException if the class of an element of this list

     *         is incompatible with the specified collection

     * (<a href="Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if this list contains a null element and the

     *         specified collection does not permit null elements

     *         (<a href="Collection.html#optional-restrictions">optional</a>),

     *         or if the specified collection is null

     * @see #remove(Object)

     * @see #contains(Object)

     */

    boolean removeAll(Collection<?> c);

    /**

     * Retains only the elements in this list that are contained in the

     * specified collection (optional operation).  In other words, removes

     * from this list all of its elements that are not contained in the

     * specified collection.

     *

     * @param c collection containing elements to be retained in this list

     * @return <tt>true</tt> if this list changed as a result of the call

     * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation

     *         is not supported by this list

     * @throws ClassCastException if the class of an element of this list

     *         is incompatible with the specified collection

     * (<a href="Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if this list contains a null element and the

     *         specified collection does not permit null elements

     *         (<a href="Collection.html#optional-restrictions">optional</a>),

     *         or if the specified collection is null

     * @see #remove(Object)

     * @see #contains(Object)

     */

    boolean retainAll(Collection<?> c);

    /**

     * Removes all of the elements from this list (optional operation).

     * The list will be empty after this call returns.

     *

     * @throws UnsupportedOperationException if the <tt>clear</tt> operation

     *         is not supported by this list

     */

    void clear();

    // Comparison and hashing

    /**

     * Compares the specified object with this list for equality.  Returns

     * <tt>true</tt> if and only if the specified object is also a list, both

     * lists have the same size, and all corresponding pairs of elements in

     * the two lists are <i>equal</i>.  (Two elements <tt>e1</tt> and

     * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :

     * e1.equals(e2))</tt>.)  In other words, two lists are defined to be

     * equal if they contain the same elements in the same order.  This

     * definition ensures that the equals method works properly across

     * different implementations of the <tt>List</tt> interface.

     *

     * @param o the object to be compared for equality with this list

     * @return <tt>true</tt> if the specified object is equal to this list

     */

    boolean equals(Object o);

    /**

     * Returns the hash code value for this list.  The hash code of a list

     * is defined to be the result of the following calculation:

     * <pre>

     *  int hashCode = 1;

     *  for (E e : list)

     *      hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());

     * </pre>

     * This ensures that <tt>list1.equals(list2)</tt> implies that

     * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,

     * <tt>list1</tt> and <tt>list2</tt>, as required by the general

     * contract of {@link Object#hashCode}.

     *

     * @return the hash code value for this list

     * @see Object#equals(Object)

     * @see #equals(Object)

     */

    int hashCode();

    // Positional Access Operations

    /**

     * Returns the element at the specified position in this list.

     *

     * @param index index of the element to return

     * @return the element at the specified position in this list

     * @throws IndexOutOfBoundsException if the index is out of range

     *         (<tt>index &lt; 0 || index &gt;= size()</tt>)

     */

    E get(int index);

    /**

     * Replaces the element at the specified position in this list with the

     * specified element (optional operation).

     *

     * @param index index of the element to replace

     * @param element element to be stored at the specified position

     * @return the element previously at the specified position

     * @throws UnsupportedOperationException if the <tt>set</tt> operation

     *         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 permit null elements

     * @throws IllegalArgumentException if some property of the specified

     *         element prevents it from being added to this list

     * @throws IndexOutOfBoundsException if the index is out of range

     *         (<tt>index &lt; 0 || index &gt;= size()</tt>)

     */

    E set(int index, E element);

    /**

     * Inserts the specified element at the specified position in this list

     * (optional operation).  Shifts the element currently at that position

     * (if any) and any subsequent elements to the right (adds one to their

     * indices).

     *

     * @param index index at which the specified element is to be inserted

     * @param element element to be inserted

     * @throws UnsupportedOperationException if the <tt>add</tt> operation

     *         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 permit null elements

     * @throws IllegalArgumentException if some property of the specified

     *         element prevents it from being added to this list

     * @throws IndexOutOfBoundsException if the index is out of range

     *         (<tt>index &lt; 0 || index &gt; size()</tt>)

     */

    void add(int index, E element);

    /**

     * Removes the element at the specified position in this list (optional

     * operation).  Shifts any subsequent elements to the left (subtracts one

     * from their indices).  Returns the element that was removed from the

     * list.

     *

     * @param index the index of the element to be removed

     * @return the element previously at the specified position

     * @throws UnsupportedOperationException if the <tt>remove</tt> operation

     *         is not supported by this list

     * @throws IndexOutOfBoundsException if the index is out of range

     *         (<tt>index &lt; 0 || index &gt;= size()</tt>)

     */

    E remove(int index);

    // Search Operations

    /**

     * Returns the index of the first occurrence of the specified element

     * in this list, or -1 if this list does not contain the element.

     * More formally, returns the lowest index <tt>i</tt> such that

     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,

     * or -1 if there is no such index.

     *

     * @param o element to search for

     * @return the index of the first occurrence of the specified element in

     *         this list, or -1 if this list does not contain the element

     * @throws ClassCastException if the type of the specified element

     *         is incompatible with this list

     *         (<a href="Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if the specified element is null and this

     *         list does not permit null elements

     *         (<a href="Collection.html#optional-restrictions">optional</a>)

     */

    int indexOf(Object o);

    /**

     * Returns the index of the last occurrence of the specified element

     * in this list, or -1 if this list does not contain the element.

     * More formally, returns the highest index <tt>i</tt> such that

     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,

     * or -1 if there is no such index.

     *

     * @param o element to search for

     * @return the index of the last occurrence of the specified element in

     *         this list, or -1 if this list does not contain the element