Class AbstractList<E>
- Type Parameters:
- E- the type of elements in this list
- All Implemented Interfaces:
- Iterable<E>,- Collection<E>,- List<E>,- SequencedCollection<E>
- Direct Known Subclasses:
- AbstractSequentialList,- ArrayList,- Vector
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
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Field SummaryFieldsModifier and TypeFieldDescriptionprotected intThe number of times this list has been structurally modified.
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Constructor SummaryConstructors
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Method SummaryModifier and TypeMethodDescriptionvoidInserts the specified element at the specified position in this list (optional operation).booleanAppends the specified element to the end of this list (optional operation).booleanaddAll(int index, Collection<? extends E> c) Inserts all of the elements in the specified collection into this list at the specified position (optional operation).voidclear()Removes all of the elements from this list (optional operation).booleanCompares the specified object with this list for equality.abstract Eget(int index) Returns the element at the specified position in this list.inthashCode()Returns the hash code value for this list.intReturns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.iterator()Returns an iterator over the elements in this list in proper sequence.intReturns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.Returns a list iterator over the elements in this list (in proper sequence).listIterator(int index) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.remove(int index) Removes the element at the specified position in this list (optional operation).protected voidremoveRange(int fromIndex, int toIndex) Removes from this list all of the elements whose index is betweenfromIndex, inclusive, andtoIndex, exclusive.Replaces the element at the specified position in this list with the specified element (optional operation).subList(int fromIndex, int toIndex) Returns a view of the portion of this list between the specifiedfromIndex, inclusive, andtoIndex, exclusive.Methods declared in class java.util.AbstractCollectionaddAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray, toStringMethods declared in class java.lang.Objectclone, finalize, getClass, notify, notifyAll, wait, wait, waitMethods declared in interface java.util.CollectionparallelStream, removeIf, stream, toArrayMethods declared in interface java.util.ListaddAll, addFirst, addLast, contains, containsAll, getFirst, getLast, isEmpty, remove, removeAll, removeFirst, removeLast, replaceAll, retainAll, reversed, size, sort, spliterator, toArray, toArray
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Field Details- 
modCountprotected transient int modCountThe 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 iteratorandlistIteratormethods. If the value of this field changes unexpectedly, the iterator (or list iterator) will throw aConcurrentModificationExceptionin response to thenext,remove,previous,setoraddoperations. 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)andremove(int)methods (and any other methods that it overrides that result in structural modifications to the list). A single call toadd(int, E)orremove(int)must add no more than one to this field, or the iterators (and list iterators) will throw bogusConcurrentModificationExceptions. If an implementation does not wish to provide fail-fast iterators, this field may be ignored.
 
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Constructor Details- 
AbstractListprotected AbstractList()Sole constructor. (For invocation by subclass constructors, typically implicit.)
 
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Method Details- 
addAppends 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:
- addin interface- Collection<E>
- Specified by:
- addin interface- List<E>
- Overrides:
- addin class- AbstractCollection<E>
- Implementation Requirements:
- This implementation calls add(size(), e).Note that this implementation throws an UnsupportedOperationExceptionunlessadd(int, E)is overridden.
- Parameters:
- e- element to be appended to this list
- Returns:
- true(as specified by- Collection.add(E))
- Throws:
- UnsupportedOperationException- if the- addoperation 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
 
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getReturns the element at the specified position in this list.- Specified by:
- getin interface- List<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())
 
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setReplaces the element at the specified position in this list with the specified element (optional operation).- Specified by:
- setin interface- List<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 the- setoperation 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())
 
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addInserts 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:
- addin interface- List<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 the- addoperation 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())
 
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removeRemoves 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:
- removein interface- List<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 the- removeoperation is not supported by this list
- IndexOutOfBoundsException- if the index is out of range (- index < 0 || index >= size())
 
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indexOfReturns 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 indexisuch thatObjects.equals(o, get(i)), or -1 if there is no such index.- Specified by:
- indexOfin interface- List<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)
 
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lastIndexOfReturns 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 indexisuch thatObjects.equals(o, get(i)), or -1 if there is no such index.- Specified by:
- lastIndexOfin interface- List<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)
 
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clearpublic void clear()Removes all of the elements from this list (optional operation). The list will be empty after this call returns.- Specified by:
- clearin interface- Collection<E>
- Specified by:
- clearin interface- List<E>
- Overrides:
- clearin class- AbstractCollection<E>
- Implementation Requirements:
- This implementation calls removeRange(0, size()).Note that this implementation throws an UnsupportedOperationExceptionunlessremove(int index)orremoveRange(int fromIndex, int toIndex)is overridden.
- Throws:
- UnsupportedOperationException- if the- clearoperation is not supported by this list
 
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addAllInserts 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:
- addAllin interface- List<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 UnsupportedOperationExceptionunlessadd(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:
- trueif this list changed as a result of the call
- Throws:
- UnsupportedOperationException- if the- addAlloperation 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())
 
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iteratorReturns an iterator over the elements in this list in proper sequence.- Specified by:
- iteratorin interface- Collection<E>
- Specified by:
- iteratorin interface- Iterable<E>
- Specified by:
- iteratorin interface- List<E>
- Specified by:
- iteratorin class- AbstractCollection<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 UnsupportedOperationExceptionin response to itsremovemethod 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) modCountfield.
- Returns:
- an iterator over the elements in this list in proper sequence
 
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listIteratorReturns a list iterator over the elements in this list (in proper sequence).- Specified by:
- listIteratorin interface- List<E>
- Implementation Requirements:
- This implementation returns listIterator(0).
- Returns:
- a list iterator over the elements in this list (in proper sequence)
- See Also:
 
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listIteratorReturns 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 tonext. An initial call topreviouswould return the element with the specified index minus one.- Specified by:
- listIteratorin interface- List<E>
- Implementation Requirements:
- This implementation returns a straightforward implementation of the
 ListIteratorinterface that extends the implementation of theIteratorinterface returned by theiterator()method. TheListIteratorimplementation 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 UnsupportedOperationExceptionin response to itsremove,setandaddmethods 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) modCountfield.
- Parameters:
- index- index of the first element to be returned from the list iterator (by a call to- next)
- 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())
 
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subListReturns a view of the portion of this list between the specifiedfromIndex, inclusive, andtoIndex, exclusive. (IffromIndexandtoIndexare 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: 
 Similar idioms may be constructed forlist.subList(from, to).clear();indexOfandlastIndexOf, and all of the algorithms in theCollectionsclass 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:
- subListin interface- List<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 expectedmodCountvalue of the backing list. There are two variants of the subclass, one of which implementsRandomAccess. If this list implementsRandomAccessthe 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. Theiteratormethod merely returnslistIterator(), and thesizemethod merely returns the subclass'ssizefield.All methods first check to see if the actual modCountof the backing list is equal to its expected value, and throw aConcurrentModificationExceptionif 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)
 
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equalsCompares the specified object with this list for equality. Returnstrueif 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 elementse1ande2are 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:
- equalsin interface- Collection<E>
- Specified by:
- equalsin interface- List<E>
- Overrides:
- equalsin class- Object
- 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 returnstruewhen the iterations complete.
- Parameters:
- o- the object to be compared for equality with this list
- Returns:
- trueif the specified object is equal to this list
- See Also:
 
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hashCodepublic int hashCode()Returns the hash code value for this list.- Specified by:
- hashCodein interface- Collection<E>
- Specified by:
- hashCodein interface- List<E>
- Overrides:
- hashCodein class- Object
- 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:
 
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removeRangeprotected void removeRange(int fromIndex, int toIndex) Removes from this list all of the elements whose index is betweenfromIndex, inclusive, andtoIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by(toIndex - fromIndex)elements. (IftoIndex==fromIndex, this operation has no effect.)This method is called by the clearoperation 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 theclearoperation on this list and its subLists.- Implementation Requirements:
- This implementation gets a list iterator positioned before
 fromIndex, and repeatedly callsListIterator.nextfollowed byListIterator.removeuntil the entire range has been removed. Note: ifListIterator.removerequires linear time, this implementation requires quadratic time.
- Parameters:
- fromIndex- index of first element to be removed
- toIndex- index after last element to be removed
 
 
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