AbstractList (Java 2 Platform SE 5.0) (original) (raw)

java.util

Class AbstractList

java.lang.Object java.util.AbstractCollection java.util.AbstractList

All Implemented Interfaces:

Iterable, Collection, List

Direct Known Subclasses:

AbstractSequentialList, ArrayList, Vector

public abstract class AbstractList

extends AbstractCollection

implements List

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 index) andsize() methods.

To implement a modifiable list, the programmer must additionally override the set(int index, Object element) method (which otherwise throws an UnsupportedOperationException. If the list is variable-size the programmer must additionally override the add(int index, Object element) and remove(int index) 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 the "random access" methods: get(int index), set(int index, Object element),set(int index, Object element), add(int index, Object element) and remove(int index).

The documentation for each non-abstract methods 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

See Also:

Collection, List, AbstractSequentialList, AbstractCollection

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, Object) andremove(int) methods (and any other methods that it overrides that result in structural modifications to the list). A single call toadd(int, Object) 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.

AbstractList

protected AbstractList()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

add

public boolean add(E o)

Appends the specified element to the end of this List (optional operation).

This implementation calls add(size(), o).

Note that this implementation throws anUnsupportedOperationException unless add(int, Object) is overridden.

Specified by:

[add](../../java/util/Collection.html#add%28E%29) in interface [Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Specified by:

[add](../../java/util/List.html#add%28E%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Overrides:

[add](../../java/util/AbstractCollection.html#add%28E%29) in class [AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

o - element to be appended to this list.

Returns:

true (as per the general contract ofCollection.add).

Throws:

[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") - if the add method is not supported by this Set.

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if the class of the specified element prevents it from being added to this set.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - some aspect of this element prevents it from being added to this collection.

get

public abstract E get(int index)

Returns the element at the specified position in this list.

Specified by:

[get](../../java/util/List.html#get%28int%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

index - index of element to return.

Returns:

the element at the specified position in this list.

Throws:

[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - if the given 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).

This implementation always throws anUnsupportedOperationException.

Specified by:

[set](../../java/util/List.html#set%28int, E%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

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](../../java/lang/UnsupportedOperationException.html "class in java.lang") - if the set method is not supported by this List.

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if the class of the specified element prevents it from being added to this list.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if some aspect of the specified element prevents it from being added to this list.

[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - if the specified 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).

This implementation always throws an UnsupportedOperationException.

Specified by:

[add](../../java/util/List.html#add%28int, E%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

index - index at which the specified element is to be inserted.

element - element to be inserted.

Throws:

[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") - if the add method is not supported by this list.

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if the class of the specified element prevents it from being added to this list.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if some aspect of the specified element prevents it from being added to this list.

[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - 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.

This implementation always throws anUnsupportedOperationException.

Specified by:

[remove](../../java/util/List.html#remove%28int%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

index - the index of the element to remove.

Returns:

the element previously at the specified position.

Throws:

[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") - if the remove method is not supported by this list.

[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - if the specified index is out of range (index < 0 || index >= size()).

indexOf

public int indexOf(Object o)

Returns the index in this list of the first occurence of the specified element, or -1 if the list does not contain this 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.

This implementation first gets a list iterator (withlistIterator()). Then, it iterates over the list until the specified element is found or the end of the list is reached.

Specified by:

[indexOf](../../java/util/List.html#indexOf%28java.lang.Object%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

o - element to search for.

Returns:

the index in this List of the first occurence of the specified element, or -1 if the List does not contain this element.

lastIndexOf

public int lastIndexOf(Object o)

Returns the index in this list of the last occurence of the specified element, or -1 if the list does not contain this 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.

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.

Specified by:

[lastIndexOf](../../java/util/List.html#lastIndexOf%28java.lang.Object%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

o - element to search for.

Returns:

the index in this list of the last occurence of the specified element, or -1 if the list does not contain this element.

clear

public void clear()

Removes all of the elements from this collection (optional operation). The collection will be empty after this call returns (unless it throws an exception).

This implementation calls removeRange(0, size()).

Note that this implementation throws anUnsupportedOperationException unless remove(int index) or removeRange(int fromIndex, int toIndex) is overridden.

Specified by:

[clear](../../java/util/Collection.html#clear%28%29) in interface [Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Specified by:

[clear](../../java/util/List.html#clear%28%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Overrides:

[clear](../../java/util/AbstractCollection.html#clear%28%29) in class [AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Throws:

[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") - if the clear method is not supported by this Collection.

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 the list in the order that they are returned by the specified collection's iterator. The behavior of this operation is unspecified 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.)

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, usingadd(int, Object). Many implementations will override this method for efficiency.

Note that this implementation throws anUnsupportedOperationException unless add(int, Object) is overridden.

Specified by:

[addAll](../../java/util/List.html#addAll%28int, java.util.Collection%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

index - index at which to insert the 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](../../java/lang/UnsupportedOperationException.html "class in java.lang") - if the addAll method is not supported by this list.

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if the class of an element of the specified collection prevents it from being added to this List.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - some aspect an element of the specified collection prevents it from being added to this List.

[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - index out of range (index < 0 || index > size()).

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection is null.

iterator

public Iterator<E> iterator()

Returns an iterator over the elements in this list in proper sequence.

This implementation returns a straightforward implementation of the iterator interface, relying on the backing list's size(),get(int), and remove(int) methods.

Note that the iterator returned by this method will throw anUnsupportedOperationException in response to itsremove method unless the list's remove(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.

Specified by:

[iterator](../../java/lang/Iterable.html#iterator%28%29) in interface [Iterable](../../java/lang/Iterable.html "interface in java.lang")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Specified by:

[iterator](../../java/util/Collection.html#iterator%28%29) in interface [Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Specified by:

[iterator](../../java/util/List.html#iterator%28%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Specified by:

[iterator](../../java/util/AbstractCollection.html#iterator%28%29) in class [AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Returns:

an iterator over the elements in this list in proper sequence.

See Also:

modCount

listIterator

public ListIterator<E> listIterator()

Returns an iterator of the elements in this list (in proper sequence). This implementation returns listIterator(0).

Specified by:

[listIterator](../../java/util/List.html#listIterator%28%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Returns:

an iterator of the elements in this list (in proper sequence).

See Also:

listIterator(int)

listIterator

public ListIterator<E> listIterator(int index)

Returns a list iterator of 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 the next method. An initial call to the previous method would return the element with the specified index minus one.

This implementation returns a straightforward implementation of theListIterator interface that extends the implementation of theIterator interface returned by the iterator() method. The ListIterator implementation relies on the backing list'sget(int), set(int, Object), add(int, Object) and remove(int) methods.

Note that the list iterator returned by this implementation will throw an UnsupportedOperationException in response to itsremove, set and add methods unless the list's remove(int), set(int, Object), andadd(int, Object) 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.

Specified by:

[listIterator](../../java/util/List.html#listIterator%28int%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Parameters:

index - index of the 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 the list.

Throws:

[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - if the specified index is out of range (index < 0 || index > size()).

See Also:

modCount

subList

public List<E> subList(int fromIndex, int toIndex)

Returns a view of the portion of this list between fromIndex, inclusive, and toIndex, exclusive. (If fromIndex andtoIndex are equal, the returned list is empty.) The returned list is backed by this list, so 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 operating on 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 andlastIndexOf, and all of the algorithms in theCollections 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 the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)

This implementation returns a list that subclassesAbstractList. The subclass stores, in private fields, the offset of the subList within the backing list, 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 implements RandomAccess. If this list implements RandomAccess the returned list will be an instance of the subclass that implements RandomAccess.

The subclass's set(int, Object), get(int),add(int, Object), remove(int), addAll(int, Collection) and removeRange(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 returns addAll(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. The iterator method merely returns listIterator(), and the size method merely returns the subclass's size 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.

Specified by:

[subList](../../java/util/List.html#subList%28int, int%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

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](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - endpoint index value out of range(fromIndex < 0 || toIndex > size)

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - endpoint indices out of order(fromIndex > toIndex)

equals

public boolean equals(Object o)

Compares the specified object with this list for equality. Returnstrue 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 ande2 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 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 returns false; if so, it iterates over both lists, comparing corresponding pairs of elements. If any comparison returns false, this method returnsfalse. If either iterator runs out of elements before the other it returns false (as the lists are of unequal length); otherwise it returns true when the iterations complete.

Specified by:

[equals](../../java/util/Collection.html#equals%28java.lang.Object%29) in interface [Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Specified by:

[equals](../../java/util/List.html#equals%28java.lang.Object%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Overrides:

[equals](../../java/lang/Object.html#equals%28java.lang.Object%29) in class [Object](../../java/lang/Object.html "class in java.lang")

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(), Hashtable

hashCode

public int hashCode()

Returns the hash code value for this list.

This implementation uses exactly the code that is used to define the list hash function in the documentation for the List.hashCode method.

Specified by:

[hashCode](../../java/util/Collection.html#hashCode%28%29) in interface [Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Specified by:

[hashCode](../../java/util/List.html#hashCode%28%29) in interface [List](../../java/util/List.html "interface in java.util")<[E](../../java/util/AbstractList.html "type parameter in AbstractList")>

Overrides:

[hashCode](../../java/lang/Object.html#hashCode%28%29) in class [Object](../../java/lang/Object.html "class in java.lang")

Returns:

the hash code value for this list.

See Also:

Object.equals(java.lang.Object), Hashtable

removeRange

protected void removeRange(int fromIndex, int toIndex)

Removes from this list all of the elements whose index is betweenfromIndex, inclusive, and toIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the ArrayList 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.

This implementation gets a list iterator positioned beforefromIndex, and repeatedly calls ListIterator.next followed by ListIterator.remove until the entire range has been removed. Note: if ListIterator.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.

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright © 2004, 2010 Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.