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package java.util;
/**
* An ordered collection (also known as a sequence). 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.
*
* Unlike sets, lists typically allow duplicate elements. More formally,
* lists typically allow pairs of elements e1 and e2
* such that 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 List interface places additional stipulations, beyond those
* specified in the Collection interface, on the contracts of the
* iterator, add, remove, equals, and
* hashCode methods. Declarations for other inherited methods are
* also included here for convenience.
*
* The 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 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 List interface provides a special iterator, called a
* ListIterator, that allows element insertion and replacement, and
* bidirectional access in addition to the normal operations that the
* Iterator interface provides. A method is provided to obtain a
* list iterator that starts at a specified position in the list.
*
* The 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 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 equals and 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
* NullPointerException or 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.
*
*
This interface is a member of the
*
* Java Collections Framework.
*
* @param 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 extends Collection {
// Query Operations
/**
* Returns the number of elements in this list. If this list contains
* more than Integer.MAX_VALUE elements, returns
* Integer.MAX_VALUE.
*
* @return the number of elements in this list
*/
int size();
/**
* Returns true if this list contains no elements.
*
* @return true if this list contains no elements
*/
boolean isEmpty();
/**
* Returns true if this list contains the specified element.
* More formally, returns true if and only if this list contains
* at least one element e such that
* (o==null ? e==null : o.equals(e)).
*
* @param o element whose presence in this list is to be tested
* @return true 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 permit 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 (from first to last element).
*
* 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 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 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 String:
*
*
* String[] y = x.toArray(new String[0]);
*
* Note that toArray(new Object[0]) is identical in function to
* 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
*/
T[] toArray(T[] a);
// Modification Operations
/**
* Appends the specified element to the end of this list (optional
* operation).
*
* 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 true (as specified by {@link Collection#add})
* @throws UnsupportedOperationException if the 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 i such that
* (o==null ? get(i)==null : o.equals(get(i)))
* (if such an element exists). Returns 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 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 remove operation
* is not supported by this list
*/
boolean remove(Object o);
// Bulk Modification Operations
/**
* Returns 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 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 true if this list changed as a result of the call
* @throws UnsupportedOperationException if the 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 true if this list changed as a result of the call
* @throws UnsupportedOperationException if the 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
* (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 true if this list changed as a result of the call
* @throws UnsupportedOperationException if the 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 true if this list changed as a result of the call
* @throws UnsupportedOperationException if the 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);
/**
* Removes all of the elements from this list (optional operation).
* The list will be empty after this call returns.
*
* @throws UnsupportedOperationException if the clear operation
* is not supported by this list
*/
void clear();
// Comparison and hashing
/**
* Compares the specified object with this list for equality. Returns
* true 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 equal. (Two elements e1 and
* e2 are equal if (e1==null ? e2==null :
* e1.equals(e2)).) 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 List interface.
*
* @param o the object to be compared for equality with this list
* @return true 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:
*
* int hashCode = 1;
* for (E e : list)
* hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
*
* This ensures that list1.equals(list2) implies that
* list1.hashCode()==list2.hashCode() for any two lists,
* list1 and 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
* (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 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
* (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 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
* (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 remove operation
* is not supported by this list
* @throws IndexOutOfBoundsException if the index is out of range
* (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 i such that
* (o==null ? get(i)==null : o.equals(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 i such that
* (o==null ? get(i)==null : o.equals(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 listIterator();
/**
* Returns a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list.
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
*
* @param index index of the first element to be returned from the
* list iterator (by a call to {@link ListIterator#next next})
* @return a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list
* @throws IndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index > size()})
*/
ListIterator listIterator(int index);
// View
/**
* Returns a view of the portion of this list between the specified
* fromIndex, inclusive, and toIndex, exclusive. (If
* fromIndex and toIndex are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations supported
* by this list.
*
* 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:
*
* list.subList(from, to).clear();
*
* Similar idioms may be constructed for indexOf and
* lastIndexOf, and all of the algorithms in the
* Collections class can be applied to a subList.
*
* 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
* (fromIndex < 0 || toIndex > size ||
* fromIndex > toIndex)
*/
List subList(int fromIndex, int toIndex);
}