Class AbstractList<E>
- java.lang.Object
-
- java.util.AbstractCollection<E>
-
- java.util.AbstractList<E>
- All Implemented Interfaces:
-
Iterable<E>
,Collection<E>
,List<E>
- Direct Known Subclasses:
-
AbstractSequentialList
,ArrayList
,Vector
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E>
This class provides a skeletal implementation of the List
interface to minimize the effort required to implement this interface backed by a "random access" data store (such as an array). For sequential access data (such as a linked list), AbstractSequentialList
should be used in preference to this class.
To implement an unmodifiable list, the programmer needs only to extend this class and provide implementations for the get(int)
and size()
methods.
To implement a modifiable list, the programmer must additionally override the set(int, E)
method (which otherwise throws an UnsupportedOperationException
). If the list is variable-size the programmer must additionally override the add(int, E)
and remove(int)
methods.
The programmer should generally provide a void (no argument) and collection constructor, as per the recommendation in the Collection
interface specification.
Unlike the other abstract collection implementations, the programmer does not have to provide an iterator implementation; the iterator and list iterator are implemented by this class, on top of the "random access" methods: get(int)
, set(int, E)
, add(int, E)
and remove(int)
.
The documentation for each non-abstract method in this class describes its implementation in detail. Each of these methods may be overridden if the collection being implemented admits a more efficient implementation.
This class is a member of the Java Collections Framework.
- Since:
- 1.2
Field Summary
Modifier and Type | Field | Description |
---|---|---|
protected int | modCount | The number of times this list has been structurally modified. |
Constructor Summary
Modifier | Constructor | Description |
---|---|---|
protected | AbstractList() | Sole constructor. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | add(int index,
E element) | Inserts the specified element at the specified position in this list (optional operation). |
boolean | add(E e) | Appends the specified element to the end of this list (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 | equals(Object o) | Compares the specified object with this list for equality. |
abstract 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 of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. |
Iterator<E> | iterator() | Returns an iterator over the elements in this list in proper sequence. |
int | lastIndexOf(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. |
ListIterator<E> | listIterator() | Returns a list iterator over the elements in this list (in proper sequence). |
ListIterator<E> | listIterator(int index) | Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. |
E | remove(int index) | Removes the element at the specified position in this list (optional operation). |
protected void | removeRange(int fromIndex,
int toIndex) | Removes from this list all of the elements whose index is between |
E | set(int index,
E element) | Replaces the element at the specified position in this list with the specified element (optional operation). |
List<E> | subList(int fromIndex,
int toIndex) | Returns a view of the portion of this list between the specified |
Methods declared in class java.util.AbstractCollection
addAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray, toString
Methods declared in class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
parallelStream, removeIf, stream, toArray
Methods declared in interface java.lang.Iterable
forEach
Methods declared in interface java.util.List
addAll, contains, containsAll, isEmpty, remove, removeAll, replaceAll, retainAll, size, sort, spliterator, toArray, toArray
Field Detail
modCount
protected transient int modCount
The number of times this list has been structurally modified. Structural modifications are those that change the size of the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.
This field is used by the iterator and list iterator implementation returned by the iterator
and listIterator
methods. If the value of this field changes unexpectedly, the iterator (or list iterator) will throw a ConcurrentModificationException
in response to the next
, remove
, previous
, set
or add
operations. This provides fail-fast behavior, rather than non-deterministic behavior in the face of concurrent modification during iteration.
Use of this field by subclasses is optional. If a subclass wishes to provide fail-fast iterators (and list iterators), then it merely has to increment this field in its add(int, E)
and remove(int)
methods (and any other methods that it overrides that result in structural modifications to the list). A single call to add(int, E)
or remove(int)
must add no more than one to this field, or the iterators (and list iterators) will throw bogus ConcurrentModificationExceptions
. If an implementation does not wish to provide fail-fast iterators, this field may be ignored.
Constructor Detail
AbstractList
protected AbstractList()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Method Detail
add
public boolean add(E e)
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.
- Specified by:
-
add
in interfaceCollection<E>
- Specified by:
-
add
in interfaceList<E>
- Overrides:
-
add
in classAbstractCollection<E>
- Implementation Requirements:
- This implementation calls
add(size(), e)
.Note that this implementation throws an
UnsupportedOperationException
unlessadd(int, E)
is overridden. - Parameters:
-
e
- element to be appended to this list - Returns:
-
true
(as specified byCollection.add(E)
) - Throws:
-
UnsupportedOperationException
- if theadd
operation 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 permit null elements -
IllegalArgumentException
- if some property of this element prevents it from being added to this list
get
public abstract E get(int index)
Returns the element at the specified position in this list.
- Specified by:
-
get
in interfaceList<E>
- Parameters:
-
index
- index of the 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()
)
set
public E set(int index, E element)
Replaces the element at the specified position in this list with the specified element (optional operation).
- Specified by:
-
set
in interfaceList<E>
- Implementation Requirements:
- This implementation always throws an
UnsupportedOperationException
. - Parameters:
-
index
- index of the element to replace -
element
- element to be stored at the specified position - Returns:
- the element previously at the specified position
- Throws:
-
UnsupportedOperationException
- if theset
operation 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 permit null elements -
IllegalArgumentException
- if some property of the specified element prevents it from being added to this list -
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
add
public void add(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).
- Specified by:
-
add
in interfaceList<E>
- Implementation Requirements:
- This implementation always throws an
UnsupportedOperationException
. - Parameters:
-
index
- index at which the specified element is to be inserted -
element
- element to be inserted - Throws:
-
UnsupportedOperationException
- if theadd
operation 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 permit null elements -
IllegalArgumentException
- if some property of the specified element prevents it from being added to this list -
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)
remove
public E remove(int index)
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.
- Specified by:
-
remove
in interfaceList<E>
- Implementation Requirements:
- This implementation always throws an
UnsupportedOperationException
. - Parameters:
-
index
- the index of the element to be removed - Returns:
- the element previously at the specified position
- Throws:
-
UnsupportedOperationException
- if theremove
operation is not supported by this list -
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
indexOf
public int indexOf(Object o)
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 Objects.equals(o, get(i))
, or -1 if there is no such index.
- Specified by:
-
indexOf
in interfaceList<E>
- Implementation Requirements:
- This implementation first gets a list iterator (with
listIterator()
). Then, it iterates over the list until the specified element is found or the end of the list is reached. - Parameters:
-
o
- element to search for - Returns:
- 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) -
NullPointerException
- if the specified element is null and this list does not permit null elements (optional)
lastIndexOf
public int lastIndexOf(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 Objects.equals(o, get(i))
, or -1 if there is no such index.
- Specified by:
-
lastIndexOf
in interfaceList<E>
- Implementation Requirements:
- This implementation first gets a list iterator that points to the end of the list (with
listIterator(size())
). Then, it iterates backwards over the list until the specified element is found, or the beginning of the list is reached. - Parameters:
-
o
- element to search for - Returns:
- 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) -
NullPointerException
- if the specified element is null and this list does not permit null elements (optional)
clear
public void clear()
Removes all of the elements from this list (optional operation). The list will be empty after this call returns.
- Specified by:
-
clear
in interfaceCollection<E>
- Specified by:
-
clear
in interfaceList<E>
- Overrides:
-
clear
in classAbstractCollection<E>
- Implementation Requirements:
- This implementation calls
removeRange(0, size())
.Note that this implementation throws an
UnsupportedOperationException
unlessremove(int index)
orremoveRange(int fromIndex, int toIndex)
is overridden. - Throws:
-
UnsupportedOperationException
- if theclear
operation is not supported by this list
addAll
public 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). 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.)
- Specified by:
-
addAll
in interfaceList<E>
- Implementation Requirements:
- This implementation gets an iterator over the specified collection and iterates over it, inserting the elements obtained from the iterator into this list at the appropriate position, one at a time, using
add(int, E)
. Many implementations will override this method for efficiency.Note that this implementation throws an
UnsupportedOperationException
unlessadd(int, E)
is overridden. - Parameters:
-
index
- index at which to insert the first element from the specified collection -
c
- collection containing elements to be added to this list - Returns:
-
true
if this list changed as a result of the call - Throws:
-
UnsupportedOperationException
- if theaddAll
operation is not supported by this list -
ClassCastException
- if the class of an element 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 permit null elements, or if the specified collection is null -
IllegalArgumentException
- if some property of an element of the specified collection prevents it from being added to this list -
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)
iterator
public Iterator<E> iterator()
Returns an iterator over the elements in this list in proper sequence.
- Specified by:
-
iterator
in interfaceCollection<E>
- Specified by:
-
iterator
in interfaceIterable<E>
- Specified by:
-
iterator
in interfaceList<E>
- Specified by:
-
iterator
in classAbstractCollection<E>
- Implementation Requirements:
- This implementation returns a straightforward implementation of the iterator interface, relying on the backing list's
size()
,get(int)
, andremove(int)
methods.Note that the iterator returned by this method will throw an
UnsupportedOperationException
in response to itsremove
method unless the list'sremove(int)
method is overridden.This implementation can be made to throw runtime exceptions in the face of concurrent modification, as described in the specification for the (protected)
modCount
field. - Returns:
- an iterator over the elements in this list in proper sequence
listIterator
public ListIterator<E> listIterator()
Returns a list iterator over the elements in this list (in proper sequence).
- Specified by:
-
listIterator
in interfaceList<E>
- Implementation Requirements:
- This implementation returns
listIterator(0)
. - Returns:
- a list iterator over the elements in this list (in proper sequence)
- See Also:
listIterator(int)
listIterator
public ListIterator<E> listIterator(int index)
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 next
. An initial call to previous
would return the element with the specified index minus one.
- Specified by:
-
listIterator
in interfaceList<E>
- Implementation Requirements:
- This implementation returns a straightforward implementation of the
ListIterator
interface that extends the implementation of theIterator
interface returned by theiterator()
method. TheListIterator
implementation relies on the backing list'sget(int)
,set(int, E)
,add(int, E)
andremove(int)
methods.Note that the list iterator returned by this implementation will throw an
UnsupportedOperationException
in response to itsremove
,set
andadd
methods unless the list'sremove(int)
,set(int, E)
, andadd(int, E)
methods are overridden.This implementation can be made to throw runtime exceptions in the face of concurrent modification, as described in the specification for the (protected)
modCount
field. - Parameters:
-
index
- index of the first element to be returned from the list iterator (by a call tonext
) - Returns:
- 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 (index < 0 || index > size()
)
subList
public List<E> subList(int fromIndex, int toIndex)
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.)
- Specified by:
-
subList
in interfaceList<E>
- Implementation Requirements:
- This implementation returns a list that subclasses
AbstractList
. The subclass stores, in private fields, the size of the subList (which can change over its lifetime), and the expectedmodCount
value of the backing list. There are two variants of the subclass, one of which implementsRandomAccess
. If this list implementsRandomAccess
the returned list will be an instance of the subclass that implementsRandomAccess
.The subclass's
set(int, E)
,get(int)
,add(int, E)
,remove(int)
,addAll(int, Collection)
andremoveRange(int, int)
methods all delegate to the corresponding methods on the backing abstract list, after bounds-checking the index and adjusting for the offset. TheaddAll(Collection c)
method merely returnsaddAll(size, c)
.The
listIterator(int)
method returns a "wrapper object" over a list iterator on the backing list, which is created with the corresponding method on the backing list. Theiterator
method merely returnslistIterator()
, and thesize
method merely returns the subclass'ssize
field.All methods first check to see if the actual
modCount
of the backing list is equal to its expected value, and throw aConcurrentModificationException
if it is not. - 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
- if an endpoint index value is out of range(fromIndex < 0 || toIndex > size)
-
IllegalArgumentException
- if the endpoint indices are out of order(fromIndex > toIndex)
equals
public boolean equals(Object o)
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.
- Specified by:
-
equals
in interfaceCollection<E>
- Specified by:
-
equals
in interfaceList<E>
- Overrides:
-
equals
in classObject
- Implementation Requirements:
- This implementation first checks if the specified object is this list. If so, it returns
true
; if not, it checks if the specified object is a list. If not, it returnsfalse
; if so, it iterates over both lists, comparing corresponding pairs of elements. If any comparison returnsfalse
, this method returnsfalse
. If either iterator runs out of elements before the other it returnsfalse
(as the lists are of unequal length); otherwise it returnstrue
when the iterations complete. - Parameters:
-
o
- the object to be compared for equality with this list - Returns:
-
true
if the specified object is equal to this list - See Also:
-
Object.hashCode()
,HashMap
hashCode
public int hashCode()
Returns the hash code value for this list.
- Specified by:
-
hashCode
in interfaceCollection<E>
- Specified by:
-
hashCode
in interfaceList<E>
- Overrides:
-
hashCode
in classObject
- Implementation Requirements:
- This implementation uses exactly the code that is used to define the list hash function in the documentation for the
List.hashCode()
method. - Returns:
- the hash code value for this list
- See Also:
-
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
removeRange
protected void removeRange(int fromIndex, int toIndex)
Removes from this list all of the elements whose index is between fromIndex
, inclusive, and toIndex
, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by (toIndex - fromIndex)
elements. (If toIndex==fromIndex
, this operation has no effect.)
This method is called by the clear
operation on this list and its subLists. Overriding this method to take advantage of the internals of the list implementation can substantially improve the performance of the clear
operation on this list and its subLists.
- Implementation Requirements:
- This implementation gets a list iterator positioned before
fromIndex
, and repeatedly callsListIterator.next
followed byListIterator.remove
until the entire range has been removed. Note: ifListIterator.remove
requires linear time, this implementation requires quadratic time. - Parameters:
-
fromIndex
- index of first element to be removed -
toIndex
- index after last element to be removed