java.util
public interface List<E> extends Collection<E>
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 a 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.
Since: 1.2
Version: 1.43, 06/22/03
See Also: Collection Set ArrayList LinkedList Vector Arrays Collections EMPTY_LIST AbstractList AbstractSequentialList
| Method Summary | |
|---|---|
| boolean | add(E o)
Appends the specified element to the end of this list (optional
operation). |
| void | add(int index, E element)
Inserts the specified element at the specified position in this list
(optional operation). |
| boolean | addAll(Collection<? extends E> 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). |
| boolean | addAll(int index, Collection<? extends E> c)
Inserts all of the elements in the specified collection into this
list at the specified position (optional operation). |
| void | clear()
Removes all of the elements from this list (optional operation). |
| boolean | contains(Object o)
Returns true if this list contains the specified element.
|
| boolean | containsAll(Collection<?> c)
Returns true if this list contains all of the elements of the
specified collection.
|
| boolean | equals(Object o)
Compares the specified object with this list for equality. |
| E | get(int index)
Returns the element at the specified position in this list.
|
| int | hashCode()
Returns the hash code value for this list. |
| int | indexOf(Object o)
Returns the index in this list of the first occurrence of the specified
element, or -1 if this list does not contain this element.
|
| boolean | isEmpty()
Returns true if this list contains no elements.
|
| Iterator<E> | iterator()
Returns an iterator over the elements in this list in proper sequence.
|
| int | lastIndexOf(Object o)
Returns the index in this list of the last occurrence of the specified
element, or -1 if this list does not contain this element.
|
| ListIterator<E> | listIterator()
Returns a list iterator of the elements in this list (in proper
sequence).
|
| ListIterator<E> | listIterator(int index)
Returns a list iterator of the elements in this list (in proper
sequence), starting at the specified position in this list. |
| boolean | remove(Object o)
Removes the first occurrence in this list of the specified element
(optional operation). |
| E | remove(int index)
Removes the element at the specified position in this list (optional
operation). |
| boolean | removeAll(Collection<?> c)
Removes from this list all the elements that are contained in the
specified collection (optional operation).
|
| boolean | retainAll(Collection<?> c)
Retains only the elements in this list that are contained in the
specified collection (optional operation). |
| E | set(int index, E element)
Replaces the element at the specified position in this list with the
specified element (optional operation).
|
| int | size()
Returns the number of elements in this list. |
| List<E> | subList(int fromIndex, int toIndex)
Returns a view of the portion of this list between the specified
fromIndex, inclusive, and toIndex, exclusive. |
| Object[] | toArray()
Returns an array containing all of the elements in this list in proper
sequence. |
| <T> T[] | toArray(T[] a)
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. |
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.
Parameters: o element to be appended to this list.
Returns: true (as per the general contract of the Collection.add method).
Throws: UnsupportedOperationException if the add method is not supported by this list. ClassCastException if the class of the specified element prevents it from being added to this list. NullPointerException if the specified element is null and this list does not support null elements. IllegalArgumentException if some aspect of this element prevents it from being added to this list.
Parameters: index index at which the specified element is to be inserted. element element to be inserted.
Throws: UnsupportedOperationException if the add method is not supported by this list. ClassCastException if the class of the specified element prevents it from being added to this list. NullPointerException if the specified element is null and this list does not support null elements. IllegalArgumentException if some aspect of the specified element prevents it from being added to this list. IndexOutOfBoundsException if the index is out of range (index < 0 || index > size()).
Parameters: c collection whose elements are to be added to this list.
Returns: true if this list changed as a result of the call.
Throws: UnsupportedOperationException if the addAll method is not supported by this list. ClassCastException if the class of an element in the specified collection prevents it from being added to this list. 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 null. IllegalArgumentException if some aspect of an element in the specified collection prevents it from being added to this list.
See Also: add
Parameters: index index at which to insert first element from the specified collection. c elements to be inserted into this list.
Returns: true if this list changed as a result of the call.
Throws: UnsupportedOperationException if the addAll method is not supported by this list. ClassCastException if the class of one of elements of the specified collection prevents it from being added to this list. 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 null. IllegalArgumentException if some aspect of one of elements of the specified collection prevents it from being added to this list. IndexOutOfBoundsException if the index is out of range (index < 0 || index > size()).
Throws: UnsupportedOperationException if the clear method is not supported by this list.
Parameters: o element whose presence in this list is to be tested.
Returns: true if this list contains the specified element.
Throws: ClassCastException if the type of the specified element is incompatible with this list (optional). NullPointerException if the specified element is null and this list does not support null elements (optional).
Parameters: c collection to be checked for containment in this list.
Returns: 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). NullPointerException if the specified collection contains one or more null elements and this list does not support null elements (optional). NullPointerException if the specified collection is null.
See Also: contains
Parameters: o the object to be compared for equality with this list.
Returns: true if the specified object is equal to this list.
Parameters: index index of element to return.
Returns: the element at the specified position in this list.
Throws: IndexOutOfBoundsException if the index is out of range (index < 0 || index >= size()).
hashCode = 1;
Iterator i = list.iterator();
while (i.hasNext()) {
Object obj = i.next();
hashCode = 31*hashCode + (obj==null ? 0 : obj.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 Object.hashCode.
Returns: the hash code value for this list.
Parameters: o element to search for.
Returns: the index in this list of the first occurrence of the specified element, or -1 if this list does not contain this element.
Throws: ClassCastException if the type of the specified element is incompatible with this list (optional). NullPointerException if the specified element is null and this list does not support null elements (optional).
Returns: true if this list contains no elements.
Returns: an iterator over the elements in this list in proper sequence.
Parameters: o element to search for.
Returns: the index in this list of the last occurrence of the specified element, or -1 if this list does not contain this element.
Throws: ClassCastException if the type of the specified element is incompatible with this list (optional). NullPointerException if the specified element is null and this list does not support null elements (optional).
Returns: a list iterator of the elements in this list (in proper sequence).
Parameters: index index of first element to be returned from the list iterator (by a call to the next method).
Returns: a list iterator of the elements in this list (in proper sequence), starting at the specified position in this list.
Throws: IndexOutOfBoundsException if the index is out of range (index < 0 || index > size()).
Parameters: o element to be removed from this list, if present.
Returns: true if this list contained the specified element.
Throws: ClassCastException if the type of the specified element is incompatible with this list (optional). NullPointerException if the specified element is null and this list does not support null elements (optional). UnsupportedOperationException if the remove method is not supported by this list.
Parameters: index the index of the element to removed.
Returns: the element previously at the specified position.
Throws: UnsupportedOperationException if the remove method is not supported by this list. IndexOutOfBoundsException if the index is out of range (index < 0 || index >= size()).
Parameters: c collection that defines which elements will be removed from this list.
Returns: true if this list changed as a result of the call.
Throws: UnsupportedOperationException if the removeAll method is not supported by this list. ClassCastException if the types of one or more elements in this list are incompatible with the specified collection (optional). NullPointerException if this list contains one or more null elements and the specified collection does not support null elements (optional). NullPointerException if the specified collection is null.
Parameters: c collection that defines which elements this set will retain.
Returns: true if this list changed as a result of the call.
Throws: UnsupportedOperationException if the retainAll method is not supported by this list. ClassCastException if the types of one or more elements in this list are incompatible with the specified collection (optional). NullPointerException if this list contains one or more null elements and the specified collection does not support null elements (optional). NullPointerException if the specified collection is null.
Parameters: index index of element to replace. element element to be stored at the specified position.
Returns: the element previously at the specified position.
Throws: UnsupportedOperationException if the set method is not supported by this list. ClassCastException if the class of the specified element prevents it from being added to this list. NullPointerException if the specified element is null and this list does not support null elements. IllegalArgumentException if some aspect of the specified element prevents it from being added to this list. IndexOutOfBoundsException if the index is out of range (index < 0 || index >= size()).
Returns: the number of elements in 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.)
Parameters: fromIndex low endpoint (inclusive) of the subList. toIndex high endpoint (exclusive) of the subList.
Returns: a view of the specified range within this list.
Throws: IndexOutOfBoundsException for an illegal endpoint index value (fromIndex < 0 || toIndex > size || fromIndex > toIndex).
Returns: an array containing all of the elements in this list in proper sequence.
See Also: Arrays
Parameters: 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.
Returns: 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. NullPointerException if the specified array is null.