* * Unlike sets, lists typically allow duplicate elements. More formally, * lists typically allow pairs of elements {@code e1} and {@code e2} * such that {@code e1.equals(e2)}, 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.
* * The {@code List} interface places additional stipulations, beyond those * specified in the {@code Collection} interface, on the contracts of the * {@code iterator}, {@code add}, {@code remove}, {@code equals}, and * {@code hashCode} methods. Declarations for other inherited methods are * also included here for convenience.
* * The {@code List} 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 {@code LinkedList} 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.
* * The {@code List} interface provides a special iterator, called a * {@code ListIterator}, that allows element insertion and replacement, and * bidirectional access in addition to the normal operations that the * {@code Iterator} interface provides. A method is provided to obtain a * list iterator that starts at a specified position in the list.
* * The {@code List} 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.
* * The {@code List} interface provides two methods to efficiently insert and * remove multiple elements at an arbitrary point in the list.
* * Note: While it is permissible for lists to contain themselves as elements, * extreme caution is advised: the {@code equals} and {@code hashCode} * methods are no longer well defined on such a list. * *
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 * {@code NullPointerException} or {@code ClassCastException}. 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. * *
The {@link List#of(Object...) List.of} and * {@link List#copyOf List.copyOf} static factory methods * provide a convenient way to create unmodifiable lists. The {@code List} * instances created by these methods have the following characteristics: * *
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. * *
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. * *
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 {@code null}. * (This is useful in determining the length of the list only if * the caller knows that the list does not contain any null elements.) * *
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. * *
Suppose {@code x} is a list known to contain only strings. * The following code can be used to dump the list into a newly * allocated array of {@code String}: * *
{@code
* String[] y = x.toArray(new String[0]);
* }
*
* Note that {@code toArray(new Object[0])} is identical in function to
* {@code toArray()}.
*
* @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
*/
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 {@code true} (as specified by {@link Collection#add}) * @throws UnsupportedOperationException if the {@code add} 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 {@code i} such that * {@code Objects.equals(o, get(i))} * (if such an element exists). Returns {@code true} 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 {@code true} 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 permit null elements * (optional) * @throws UnsupportedOperationException if the {@code remove} operation * is not supported by this list */ boolean remove(Object o); // Bulk Modification Operations /** * Returns {@code true} if this list contains all of the elements of the * specified collection. * * @param c collection to be checked for containment in this list * @return {@code true} 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 permit null * elements * (optional), * 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 {@code true} if this list changed as a result of the call * @throws UnsupportedOperationException if the {@code addAll} 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 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 {@code true} if this list changed as a result of the call * @throws UnsupportedOperationException if the {@code addAll} 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 * ({@code index < 0 || index > size()}) */ boolean addAll(int index, Collection 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 {@code true} if this list changed as a result of the call * @throws UnsupportedOperationException if the {@code removeAll} operation * is not supported by this list * @throws ClassCastException if the class of an element of this list * is incompatible with the specified collection * (optional) * @throws NullPointerException if this list 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); /** * 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 {@code true} if this list changed as a result of the call * @throws UnsupportedOperationException if the {@code retainAll} operation * is not supported by this list * @throws ClassCastException if the class of an element of this list * is incompatible with the specified collection * (optional) * @throws NullPointerException if this list 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 retainAll(Collection c); /** * Replaces each element of this list with the result of applying the * operator to that element. Errors or runtime exceptions thrown by * the operator are relayed to the caller. * * @implSpec * The default implementation is equivalent to, for this {@code list}: *
{@code
* final ListIterator li = list.listIterator();
* while (li.hasNext()) {
* li.set(operator.apply(li.next()));
* }
* }
*
* If the list's list-iterator does not support the {@code set} operation
* then an {@code UnsupportedOperationException} will be thrown when
* replacing the first element.
*
* @param operator the operator to apply to each element
* @throws UnsupportedOperationException if this list is unmodifiable.
* Implementations may throw this exception if an element
* cannot be replaced or if, in general, modification is not
* supported
* @throws NullPointerException if the specified operator is null or
* if the operator result is a null value and this list does
* not permit null elements
* (optional)
* @since 1.8
*/
default void replaceAll(UnaryOperatorAll elements in this list must be mutually comparable using the * specified comparator (that is, {@code c.compare(e1, e2)} must not throw * a {@code ClassCastException} for any elements {@code e1} and {@code e2} * in the list). * *
If the specified comparator is {@code null} then all elements in this * list must implement the {@link Comparable} interface and the elements' * {@linkplain Comparable natural ordering} should be used. * *
This list must be modifiable, but need not be resizable. * *
For apps running on and targeting Android versions greater than * Nougat (API level {@code > 25}), {@link Collections#sort(List)} * delegates to this method. Such apps must not call * {@link Collections#sort(List)} from this method. Instead, prefer * not overriding this method at all. If you must override it, consider * this implementation: *
* @Override
* public void sort(Comparator<? super E> c) {
* Object[] elements = toArray();
* Arrays.sort(elements, c);
* ListIterator<E> iterator = (ListIterator<Object>) listIterator();
* for (Object element : elements) {
* iterator.next();
* iterator.set((E) element);
* }
* }
*
*
* @implSpec
* The default implementation obtains an array containing all elements in
* this list, sorts the array, and iterates over this list resetting each
* element from the corresponding position in the array. (This avoids the
* n2 log(n) performance that would result from attempting
* to sort a linked list in place.)
*
* @implNote
* This implementation is a stable, adaptive, iterative mergesort that
* requires far fewer than n lg(n) comparisons when the input array is
* partially sorted, while offering the performance of a traditional
* mergesort when the input array is randomly ordered. If the input array
* is nearly sorted, the implementation requires approximately n
* comparisons. Temporary storage requirements vary from a small constant
* for nearly sorted input arrays to n/2 object references for randomly
* ordered input arrays.
*
* The implementation takes equal advantage of ascending and * descending order in its input array, and can take advantage of * ascending and descending order in different parts of the same * input array. It is well-suited to merging two or more sorted arrays: * simply concatenate the arrays and sort the resulting array. * *
The implementation was adapted from Tim Peters's list sort for Python
* (
* TimSort). It uses techniques from Peter McIlroy's "Optimistic
* Sorting and Information Theoretic Complexity", in Proceedings of the
* Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
* January 1993.
*
* @param c the {@code Comparator} used to compare list elements.
* A {@code null} value indicates that the elements'
* {@linkplain Comparable natural ordering} should be used
* @throws ClassCastException if the list contains elements that are not
* mutually comparable using the specified comparator
* @throws UnsupportedOperationException if the list's list-iterator does
* not support the {@code set} operation
* @throws IllegalArgumentException
* (optional)
* if the comparator is found to violate the {@link Comparator}
* contract
* @since 1.8
*/
@SuppressWarnings({"unchecked", "rawtypes"})
default void sort(Comparator c) {
Object[] a = this.toArray();
Arrays.sort(a, (Comparator) c);
ListIterator
*
* This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
*
*
* The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is structurally modified in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @param fromIndex low endpoint (inclusive) of the subList
* @param toIndex high endpoint (exclusive) of the subList
* @return a view of the specified range within this list
* @throws IndexOutOfBoundsException for an illegal endpoint index value
* ({@code fromIndex < 0 || toIndex > size ||
* fromIndex > toIndex})
*/
List The {@code Spliterator} reports {@link Spliterator#SIZED} and
* {@link Spliterator#ORDERED}. Implementations should document the
* reporting of additional characteristic values.
*
* @implSpec
* The default implementation creates a
* late-binding
* spliterator as follows:
* {@code
* int hashCode = 1;
* for (E e : list)
* hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
* }
* This ensures that {@code list1.equals(list2)} implies that
* {@code list1.hashCode()==list2.hashCode()} for any two lists,
* {@code list1} and {@code list2}, 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
* ({@code index < 0 || index >= size()})
*/
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 {@code set} 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
* ({@code index < 0 || index >= size()})
*/
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 {@code add} 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
* ({@code index < 0 || index > size()})
*/
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 {@code remove} operation
* is not supported by this list
* @throws IndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index >= size()})
*/
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 {@code i} such that
* {@code Objects.equals(o, get(i))},
* 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
* (optional)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* (optional)
*/
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 {@code i} such that
* {@code Objects.equals(o, get(i))},
* 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
* @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 permit null elements
* (optional)
*/
int lastIndexOf(Object o);
// List Iterators
/**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* @return a list iterator over the elements in this list (in proper
* sequence)
*/
ListIterator{@code
* list.subList(from, to).clear();
* }
* Similar idioms may be constructed for {@code indexOf} and
* {@code lastIndexOf}, and all of the algorithms in the
* {@code Collections} class can be applied to a subList.
*
*
* @implNote
* The created {@code Spliterator} additionally reports
* {@link Spliterator#SUBSIZED}.
*
* @return a {@code Spliterator} over the elements in this list
* @since 1.8
*/
@Override
default Spliterator{@code
* String[] array = ... ;
* List
*
* This will cause the {@link List#of(Object) List.of(E)} method
* to be invoked instead.
*
* @param