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Java Platform 1.2 |
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java.lang.Object
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+--java.util.AbstractCollection
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+--java.util.AbstractList
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) and size() 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.
Collection,
List,
AbstractSequentialList,
AbstractCollection| Field Summary | |
protected int |
modCount
The number of times this list has been structurally modified. |
| Constructor Summary | |
protected |
AbstractList()
Sole constructor. |
| Method Summary | |
void |
add(int index,
Object element)
Inserts the specified element at the specified position in this list (optional operation). |
boolean |
add(Object o)
Appends the specified element to the end of this List (optional operation). |
boolean |
addAll(int index,
Collection 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 collection (optional operation). |
boolean |
equals(Object o)
Compares the specified object with this list for equality. |
abstract Object |
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 occurence of the specified element, or -1 if the list does not contain this element. |
Iterator |
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 occurence of the specified element, or -1 if the list does not contain this element. |
ListIterator |
listIterator()
Returns an iterator of the elements in this list (in proper sequence). |
ListIterator |
listIterator(int index)
Returns a list iterator of the elements in this list (in proper sequence), starting at the specified position in the list. |
Object |
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 fromIndex, inclusive, and toIndex, exclusive. |
Object |
set(int index,
Object element)
Replaces the element at the specified position in this list with the specified element (optional operation). |
List |
subList(int fromIndex,
int toIndex)
Returns a view of the portion of this list between fromIndex, inclusive, and toIndex, exclusive. |
| Methods inherited from class java.util.AbstractCollection |
addAll,
contains,
containsAll,
isEmpty,
remove,
removeAll,
retainAll,
size,
toArray,
toArray,
toString |
| Methods inherited from class java.lang.Object |
clone,
finalize,
getClass,
notify,
notifyAll,
wait,
wait,
wait |
| Field Detail |
protected transient int modCount
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) 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, 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.
| Constructor Detail |
protected AbstractList()
| Method Detail |
public boolean add(Object o)
This implementation calls add(size(), o).
Note that this implementation throws an UnsupportedOperationException unless add(int, Object) is overridden.
o - element to be appended to this list.public abstract Object get(int index)
index - index of element to return.
public Object set(int index,
Object element)
This implementation always throws an UnsupportedOperationException.
index - index of element to replace.element - element to be stored at the specified position.
public void add(int index,
Object element)
This implementation always throws an UnsupportedOperationException.
index - index at which the specified element is to be inserted.element - element to be inserted.public Object remove(int index)
This implementation always throws an UnsupportedOperationException.
index - the index of the element to remove.public int indexOf(Object o)
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.
o - element to search for.public int lastIndexOf(Object o)
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.
o - element to search for.public void clear()
This implementation calls removeRange(0, size()).
Note that this implementation throws an UnsupportedOperationException unless remove(int index) or removeRange(int fromIndex, int toIndex) is overridden.
public boolean addAll(int index,
Collection c)
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, Object). Many implementations will override this method for efficiency.
Note that this implementation throws an UnsupportedOperationException unless add(int, Object) is overridden.
index - index at which to insert the first element from the
specified collection.c - elements to be inserted into this List.public Iterator iterator()
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 an UnsupportedOperationException in response to its remove 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.
modCountpublic ListIterator listIterator()
listIterator(int)public ListIterator listIterator(int index)
This implementation returns a straightforward implementation of the ListIterator interface that extends the implementation of the Iterator interface returned by the iterator() method. The ListIterator implementation relies on the backing list's get(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 its remove, set and add methods unless the list's remove(int), set(int, Object), and add(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.
index - index of the first element to be returned from the list
iterator (by a call to the next method).modCount
public 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 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();n 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 the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)
This implementation returns a list that subclasses AbstractList. 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 expected modCount value of the backing list.
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. The addAll(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 a ConcurrentModificationException if it is not.
fromIndex - low endpoint (inclusive) of the subList.toKey - high endpoint (exclusive) of the subList.public boolean equals(Object o)
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 returns false. 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.
o - the object to be compared for equality with this list.public int hashCode()
This implementation uses exactly the code that is used to define the list hash function in the documentation for the List.hashCode method.
protected void removeRange(int fromIndex,
int toIndex)
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 before fromIndex, 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.
fromIndex - index of first element to be removed.toIndex - index after last element to be removed.
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Java Platform 1.2 |
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