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/* List.java -- An ordered collection which allows indexed access

   Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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it under the terms of the GNU General Public License as published by

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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

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along with GNU Classpath; see the file COPYING.  If not, write to the

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02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

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As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

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terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

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this exception to your version of the library, but you are not

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exception statement from your version. */

package java.util;

/**

 * An ordered collection (also known as a list). This collection allows

 * access to elements by position, as well as control on where elements

 * are inserted. Unlike sets, duplicate elements are permitted by this

 * general contract (if a subclass forbids duplicates, this should be

 * documented).

 * <p>

 *

 * List places additional requirements on <code>iterator</code>,

 * <code>add</code>, <code>remove</code>, <code>equals</code>, and

 * <code>hashCode</code>, in addition to requiring more methods. List

 * indexing is 0-based (like arrays), although some implementations may

 * require time proportional to the index to obtain an arbitrary element.

 * The List interface is incompatible with Set; you cannot implement both

 * simultaneously.

 * <p>

 *

 * Lists also provide a <code>ListIterator</code> which allows bidirectional

 * traversal and other features atop regular iterators. Lists can be

 * searched for arbitrary elements, and allow easy insertion and removal

 * of multiple elements in one method call.

 * <p>

 *

 * Note: While lists may contain themselves as elements, this leads to

 * undefined (usually infinite recursive) behavior for some methods like

 * hashCode or equals.

 *

 * @author Original author unknown

 * @author Eric Blake (ebb9@email.byu.edu)

 * @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

 * @status updated to 1.4

 */

public interface List<E> extends Collection<E>

{

  /**

   * Insert an element into the list at a given position (optional operation).

   * This shifts all existing elements from that position to the end one

   * index to the right. This version of add has no return, since it is

   * assumed to always succeed if there is no exception.

   *

   * @param index the location to insert the item

   * @param o the object to insert

   * @throws UnsupportedOperationException if this list does not support the

   *         add operation

   * @throws IndexOutOfBoundsException if index < 0 || index > size()

   * @throws ClassCastException if o cannot be added to this list due to its

   *         type

   * @throws IllegalArgumentException if o cannot be added to this list for

   *         some other reason

   * @throws NullPointerException if o is null and this list doesn't support

   *         the addition of null values.

   */

  void add(int index, E o);

  /**

   * Add an element to the end of the list (optional operation). If the list

   * imposes restraints on what can be inserted, such as no null elements,

   * this should be documented.

   *

   * @param o the object to add

   * @return true, as defined by Collection for a modified list

   * @throws UnsupportedOperationException if this list does not support the

   *         add operation

   * @throws ClassCastException if o cannot be added to this list due to its

   *         type

   * @throws IllegalArgumentException if o cannot be added to this list for

   *         some other reason

   * @throws NullPointerException if o is null and this list doesn't support

   *         the addition of null values.

   */

  boolean add(E o);

  /**

   * Insert the contents of a collection into the list at a given position

   * (optional operation). Shift all elements at that position to the right

   * by the number of elements inserted. This operation is undefined if

   * this list is modified during the operation (for example, if you try

   * to insert a list into itself).

   *

   * @param index the location to insert the collection

   * @param c the collection to insert

   * @return true if the list was modified by this action, that is, if c is

   *         non-empty

   * @throws UnsupportedOperationException if this list does not support the

   *         addAll operation

   * @throws IndexOutOfBoundsException if index < 0 || index > size()

   * @throws ClassCastException if some element of c cannot be added to this

   *         list due to its type

   * @throws IllegalArgumentException if some element of c cannot be added

   *         to this list for some other reason

   * @throws NullPointerException if some element of c is null and this list

   *         doesn't support the addition of null values.

   * @throws NullPointerException if the specified collection is null

   * @see #add(int, Object)

   */

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

  /**

   * Add the contents of a collection to the end of the list (optional

   * operation).  This operation is undefined if this list is modified

   * during the operation (for example, if you try to insert a list into

   * itself).

   *

   * @param c the collection to add

   * @return true if the list was modified by this action, that is, if c is

   *         non-empty

   * @throws UnsupportedOperationException if this list does not support the

   *         addAll operation

   * @throws ClassCastException if some element of c cannot be added to this

   *         list due to its type

   * @throws IllegalArgumentException if some element of c cannot be added

   *         to this list for some other reason

   * @throws NullPointerException if the specified collection is null

   * @throws NullPointerException if some element of c is null and this list

   *         doesn't support the addition of null values.

   * @see #add(Object)

   */

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

  /**

   * Clear the list, such that a subsequent call to isEmpty() would return

   * true (optional operation).

   *

   * @throws UnsupportedOperationException if this list does not support the

   *         clear operation

   */

  void clear();

  /**

   * Test whether this list contains a given object as one of its elements.

   * This is defined as the existence of an element e such that

   * <code>o == null ? e == null : o.equals(e)</code>.

   *

   * @param o the element to look for

   * @return true if this list contains the element

   * @throws ClassCastException if the type of o is not a valid type

   *         for this list.

   * @throws NullPointerException if o is null and the list doesn't

   *         support null values.

   */

  boolean contains(Object o);

  /**

   * Test whether this list contains every element in a given collection.

   *

   * @param c the collection to test for

   * @return true if for every element o in c, contains(o) would return true

   * @throws NullPointerException if the collection is null

   * @throws ClassCastException if the type of any element in c is not a valid

   *         type for this list.

   * @throws NullPointerException if some element of c is null and this

   *         list does not support null values.

   * @see #contains(Object)

   */

  boolean containsAll(Collection<?> c);

  /**

   * Test whether this list is equal to another object. A List is defined to be

   * equal to an object if and only if that object is also a List, and the two

   * lists have the same sequence. Two lists l1 and l2 are equal if and only

   * if <code>l1.size() == l2.size()</code>, and for every integer n between 0

   * and <code>l1.size() - 1</code> inclusive, <code>l1.get(n) == null ?

   * l2.get(n) == null : l1.get(n).equals(l2.get(n))</code>.

   *

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

   * @return true if o is equal to this list

   * @see Object#equals(Object)

   * @see #hashCode()

   */

  boolean equals(Object o);

  /**

   * Get the element at a given index in this list.

   *

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

   * @return the element at index index in this list

   * @throws IndexOutOfBoundsException if index < 0 || index >= size()

   */

  E get(int index);

  /**

   * Obtains a hash code for this list. In order to obey the general

   * contract of the hashCode method of class Object, this value is

   * calculated as follows:

   *

<p><pre>hashCode = 1;

Iterator i = list.iterator();

while (i.hasNext())

{

  Object obj = i.next();

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

}</pre>

   *

   * <p>This ensures that the general contract of Object.hashCode()

   * is adhered to.

   *

   * @return the hash code of this list

   * @see Object#hashCode()

   * @see #equals(Object)

   */

  int hashCode();

  /**

   * Obtain the first index at which a given object is to be found in this

   * list.

   *

   * @param o the object to search for

   * @return the least integer n such that <code>o == null ? get(n) == null :

   *         o.equals(get(n))</code>, or -1 if there is no such index.

   * @throws ClassCastException if the type of o is not a valid

   *         type for this list.

   * @throws NullPointerException if o is null and this

   *         list does not support null values.

   */

  int indexOf(Object o);

  /**

   * Test whether this list is empty, that is, if size() == 0.

   *

   * @return true if this list contains no elements

   */

  boolean isEmpty();

  /**

   * Obtain an Iterator over this list, whose sequence is the list order.

   *

   * @return an Iterator over the elements of this list, in order

   */

  Iterator<E> iterator();

  /**

   * Obtain the last index at which a given object is to be found in this

   * list.

   *

   * @return the greatest integer n such that <code>o == null ? get(n) == null

   *         : o.equals(get(n))</code>, or -1 if there is no such index.

   * @throws ClassCastException if the type of o is not a valid

   *         type for this list.

   * @throws NullPointerException if o is null and this

   *         list does not support null values.

   */

  int lastIndexOf(Object o);

  /**

   * Obtain a ListIterator over this list, starting at the beginning.

   *

   * @return a ListIterator over the elements of this list, in order, starting

   *         at the beginning

   */

  ListIterator<E> listIterator();

  /**

   * Obtain a ListIterator over this list, starting at a given position.

   * A first call to next() would return the same as get(index), and a

   * first call to previous() would return the same as get(index - 1).

   *

   * @param index the position, between 0 and size() inclusive, to begin the

   *        iteration from

   * @return a ListIterator over the elements of this list, in order, starting

   *         at index

   * @throws IndexOutOfBoundsException if index < 0 || index > size()

   */

  ListIterator<E> listIterator(int index);

  /**

   * Remove the element at a given position in this list (optional operation).

   * Shifts all remaining elements to the left to fill the gap.

   *

   * @param index the position within the list of the object to remove

   * @return the object that was removed

   * @throws UnsupportedOperationException if this list does not support the

   *         remove operation

   * @throws IndexOutOfBoundsException if index < 0 || index >= size()

   */

  E remove(int index);

  /**

   * Remove the first occurence of an object from this list (optional

   * operation). That is, remove the first element e such that

   * <code>o == null ? e == null : o.equals(e)</code>.

   *

   * @param o the object to remove

   * @return true if the list changed as a result of this call, that is, if

   *         the list contained at least one occurrence of o

   * @throws UnsupportedOperationException if this list does not support the

   *         remove operation

   * @throws ClassCastException if the type of o is not a valid

   *         type for this list.

   * @throws NullPointerException if o is null and this

   *         list does not support removing null values.

   */

  boolean remove(Object o);

  /**

   * Remove all elements of a given collection from this list (optional

   * operation). That is, remove every element e such that c.contains(e).

   *

   * @param c the collection to filter out

   * @return true if this list was modified as a result of this call

   * @throws UnsupportedOperationException if this list does not support the

   *         removeAll operation

   * @throws NullPointerException if the collection is null

   * @throws ClassCastException if the type of any element in c is not a valid

   *         type for this list.

   * @throws NullPointerException if some element of c is null and this

   *         list does not support removing null values.

   * @see #remove(Object)

   * @see #contains(Object)

   */

  boolean removeAll(Collection<?> c);

  /**

   * Remove all elements of this list that are not contained in a given

   * collection (optional operation). That is, remove every element e such

   * that !c.contains(e).

   *

   * @param c the collection to retain

   * @return true if this list was modified as a result of this call

   * @throws UnsupportedOperationException if this list does not support the

   *         retainAll operation

   * @throws NullPointerException if the collection is null

   * @throws ClassCastException if the type of any element in c is not a valid

   *         type for this list.

   * @throws NullPointerException if some element of c is null and this

   *         list does not support retaining null values.

   * @see #remove(Object)

   * @see #contains(Object)

   */

  boolean retainAll(Collection<?> c);

  /**

   * Replace an element of this list with another object (optional operation).

   *

   * @param index the position within this list of the element to be replaced

   * @param o the object to replace it with

   * @return the object that was replaced

   * @throws UnsupportedOperationException if this list does not support the

   *         set operation

   * @throws IndexOutOfBoundsException if index < 0 || index >= size()

   * @throws ClassCastException if o cannot be added to this list due to its

   *         type

   * @throws IllegalArgumentException if o cannot be added to this list for

   *         some other reason

   * @throws NullPointerException if o is null and this

   *         list does not support null values.

   */

  E set(int index, E o);

  /**

   * Get the number of elements in this list. If the list contains more

   * than Integer.MAX_VALUE elements, return Integer.MAX_VALUE.

   *

   * @return the number of elements in the list

   */

  int size();

  /**

   * Obtain a List view of a subsection of this list, from fromIndex

   * (inclusive) to toIndex (exclusive). If the two indices are equal, the

   * sublist is empty. The returned list should be modifiable if and only

   * if this list is modifiable. Changes to the returned list should be

   * reflected in this list. If this list is structurally modified in

   * any way other than through the returned list, the result of any subsequent

   * operations on the returned list is undefined.

   *

   * @param fromIndex the index that the returned list should start from

   *        (inclusive)

   * @param toIndex the index that the returned list should go to (exclusive)

   * @return a List backed by a subsection of this list

   * @throws IndexOutOfBoundsException if fromIndex < 0

   *         || toIndex > size() || fromIndex > toIndex

   */

  List<E> subList(int fromIndex, int toIndex);

  /**

   * Copy the current contents of this list into an array.

   *

   * @return an array of type Object[] and length equal to the length of this

   *         list, containing the elements currently in this list, in order

   */

  Object[] toArray();

  /**

   * Copy the current contents of this list into an array. If the array passed

   * as an argument has length less than that of this list, an array of the

   * same run-time type as a, and length equal to the length of this list, is

   * allocated using Reflection. Otherwise, a itself is used. The elements of

   * this list are copied into it, and if there is space in the array, the

   * following element is set to null. The resultant array is returned.

   * Note: The fact that the following element is set to null is only useful

   * if it is known that this list does not contain any null elements.

   *

   * @param a the array to copy this list into

   * @return an array containing the elements currently in this list, in

   *         order

   * @throws ArrayStoreException if the type of any element of the

   *         collection is not a subtype of the element type of a

   * @throws NullPointerException if the specified array is null

   */

  <T> T[] toArray(T[] a);

}