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.
Method Detail |
int size()
boolean isEmpty()
boolean contains(java.lang.Object o)
o
- element whose presence in this list is to be tested.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).java.util.Iterator iterator()
java.lang.Object[] toArray()
T[] toArray(T[] a)
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.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.boolean add(E o)
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.
o
- element to be appended to this list.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.boolean remove(java.lang.Object o)
o
- element to be removed from this list, if present.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.boolean containsAll(java.util.Collection c)
c
- collection to be checked for containment in this list.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.boolean addAll(java.util.Collection c)
c
- collection whose elements are to be added to this list.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.boolean addAll(int index, java.util.Collection c)
index
- index at which to insert first element from the specified collection.c
- elements to be inserted into this list.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()).boolean removeAll(java.util.Collection c)
c
- collection that defines which elements will be removed from this list.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.boolean retainAll(java.util.Collection c)
c
- collection that defines which elements this set will retain.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.void clear()
UnsupportedOperationException
- if the clear method is not supported by this list.boolean equals(java.lang.Object o)
o
- the object to be compared for equality with this list.int hashCode()
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.
E get(int index)
index
- index of element to return.IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()).E set(int index, E element)
index
- index of element to replace.element
- element to be stored at the specified position.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()).void add(int index, E element)
index
- index at which the specified element is to be inserted.element
- element to be inserted.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()).E remove(int index)
index
- the index of the element to removed.UnsupportedOperationException
- if the remove method is not supported by this list.IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()).int indexOf(java.lang.Object o)
o
- element to search for.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).int lastIndexOf(java.lang.Object o)
o
- element to search for.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).java.util.ListIterator listIterator()
java.util.ListIterator listIterator(int index)
index
- index of first element to be returned from the list iterator (by a call to the next method).IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()).java.util.List subList(int fromIndex, int toIndex)
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.)
fromIndex
- low endpoint (inclusive) of the subList.toIndex
- high endpoint (exclusive) of the subList.IndexOutOfBoundsException
- for an illegal endpoint index value (fromIndex < 0 || toIndex > size || fromIndex > toIndex).