java.util.AbstractList Maven / Gradle / Ivy
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package java.util;
/**
* 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.
*
* This class is a member of the
*
* Java Collections Framework.
*
* @author Josh Bloch
* @version 1.31, 02/02/00
* @see Collection
* @see List
* @see AbstractSequentialList
* @see AbstractCollection
* @since 1.2
*/
public abstract class AbstractList extends AbstractCollection implements List
{
/**
* 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) 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.
*/
protected transient int modCount;
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractList() { }
/**
* Appends the specified element to the end of this List (optional
* operation).
*
* This implementation calls add(size(), o).
*
* Note that this implementation throws an
* UnsupportedOperationException unless add(int, Object)
* is overridden.
*
* @param o element to be appended to this list.
*
* @return true (as per the general contract of
* Collection.add).
*
* @throws UnsupportedOperationException if the add method is not
* supported by this Set.
*
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this set.
*
* @throws IllegalArgumentException some aspect of this element prevents
* it from being added to this collection.
*/
public boolean add(Object o) {
return false;
}
/**
* Returns the element at the specified position in this list.
*
* @param index index of element to return.
*
* @return the element at the specified position in this list.
* @throws IndexOutOfBoundsException if the given index is out of range
* (index < 0 || index >= size()).
*/
public abstract Object get(int index);
/**
* Replaces the element at the specified position in this list with the
* specified element (optional operation).
*
* This implementation always throws an
* UnsupportedOperationException.
*
* @param index index of element to replace.
* @param element element to be stored at the specified position.
* @return the element previously at the specified position.
*
* @throws UnsupportedOperationException if the set method is not
* supported by this List.
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list.
* @throws IllegalArgumentException if some aspect of the specified
* element prevents it from being added to this list.
*
* @throws IndexOutOfBoundsException if the specified index is out of
* range (index < 0 || index >= size()).
*/
public Object set(int index, Object element) {
return null;
}
/**
* 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.
*
* @param index index at which the specified element is to be inserted.
* @param element element to be inserted.
*
* @throws UnsupportedOperationException if the add method is not
* supported by this list.
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list.
* @throws IllegalArgumentException if some aspect of the specified
* element prevents it from being added to this list.
* @throws IndexOutOfBoundsException index is out of range (index <
* 0 || index > size()).
*/
public void add(int index, Object element) { }
/**
* 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 an
* UnsupportedOperationException.
*
* @param index the index of the element to remove.
* @return the element previously at the specified position.
*
* @throws UnsupportedOperationException if the remove method is
* not supported by this list.
* @throws IndexOutOfBoundsException if the specified index is out of
* range (index < 0 || index >= size()).
*/
public Object remove(int index) {
return null;
}
/**
* 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 (with
* listIterator()). Then, it iterates over the list until the
* specified element is found or the end of the list is reached.
*
* @param o element to search for.
*
* @return the index in this List of the first occurence of the specified
* element, or -1 if the List does not contain this element.
*/
public int indexOf(Object o) {
return 0;
}
/**
* 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.
*
* @param o element to search for.
*
* @return the index in this list of the last occurence of the specified
* element, or -1 if the list does not contain this element.
*/
public int lastIndexOf(Object o) {
return 0;
}
/**
* 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 an
* UnsupportedOperationException unless remove(int
* index) or removeRange(int fromIndex, int toIndex) is
* overridden.
*
* @throws UnsupportedOperationException if the clear method is
* not supported by this Collection.
*/
public void clear() { }
/**
* 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, 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.
*
* @return true if this list changed as a result of the call.
* @param index index at which to insert the first element from the
* specified collection.
* @param c elements to be inserted into this List.
*
* @throws UnsupportedOperationException if the addAll method is
* not supported by this list.
*
* @throws ClassCastException if the class of an element of the specified
* collection prevents it from being added to this List.
*
* @throws IllegalArgumentException some aspect an element of the
* specified collection prevents it from being added to this
* List.
*
* @throws IndexOutOfBoundsException index out of range (index < 0
* || index > size()).
*
* @throws NullPointerException if the specified collection is null.
*/
public boolean addAll(int index, Collection c) {
return false;
}
/**
* 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 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.
*
* @return an iterator over the elements in this list in proper sequence.
*
* @see #modCount
*/
public Iterator iterator() {
return null;
}
/**
* Returns an iterator of the elements in this list (in proper sequence).
* This implementation returns listIterator(0).
*
* @return an iterator of the elements in this list (in proper sequence).
*
* @see #listIterator(int)
*/
public ListIterator listIterator() {
return null;
}
/**
* 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 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.
*
* @param index index of the first element to be returned from the list
* iterator (by a call to the next method).
*
* @return a list iterator of the elements in this list (in proper
* sequence), starting at the specified position in the list.
*
* @throws IndexOutOfBoundsException if the specified index is out of
* range (index < 0 || index > size()).
*
* @see #modCount
*/
public ListIterator listIterator(int index) {
return null;
}
/**
* Returns a view of the portion of this list between 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 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 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. 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. 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.
*
* @param fromIndex low endpoint (inclusive) of the subList.
* @param toIndex high endpoint (exclusive) of the subList.
* @return a view of the specified range within this list.
* @throws IndexOutOfBoundsException endpoint index value out of range
* (fromIndex < 0 || toIndex > size)
* @throws IllegalArgumentException endpoint indices out of order
* (fromIndex > toIndex)
*/
public List subList(int fromIndex, int toIndex) {
return null;
}
/**
* 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.
*
* 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.
*
* @param o the object to be compared for equality with this list.
*
* @return true if the specified object is equal to this list.
*/
public boolean equals(Object o) {
return false;
}
/**
* 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.
*
* @return the hash code value for this list.
*/
public int hashCode() {
return 0;
}
/**
* 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 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 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.
*
* @param fromIndex index of first element to be removed.
* @param toIndex index after last element to be removed.
*/
protected void removeRange(int fromIndex, int toIndex) { }
}