- Type Parameters:
E- the type of elements in this list
- All Implemented Interfaces:
Serializable,Cloneable,Iterable<E>,Collection<E>,List<E>,RandomAccess,SequencedCollection<E>
- Direct Known Subclasses:
AttributeList,RoleList,RoleUnresolvedList
List interface. Implements
all optional list operations, and permits all elements, including
null. In addition to implementing the List interface,
this class provides methods to manipulate the size of the array that is
used internally to store the list. (This class is roughly equivalent to
Vector, except that it is unsynchronized.)
The size, isEmpty, get, set,
iterator, and listIterator operations run in constant
time. The add operation runs in amortized constant time,
that is, adding n elements requires O(n) time. All of the other operations
run in linear time (roughly speaking). The constant factor is low compared
to that for the LinkedList implementation.
Each ArrayList instance has a capacity. The capacity is
the size of the array used to store the elements in the list. It is always
at least as large as the list size. As elements are added to an ArrayList,
its capacity grows automatically. The details of the growth policy are not
specified beyond the fact that adding an element has constant amortized
time cost.
An application can increase the capacity of an ArrayList instance
before adding a large number of elements using the ensureCapacity
operation. This may reduce the amount of incremental reallocation.
Note that this implementation is not synchronized.
If multiple threads access an ArrayList instance concurrently,
and at least one of the threads modifies the list structurally, it
must be synchronized externally. (A structural modification is
any operation that adds or deletes one or more elements, or explicitly
resizes the backing array; merely setting the value of an element is not
a structural modification.) This is typically accomplished by
synchronizing on some object that naturally encapsulates the list.
If no such object exists, the list should be "wrapped" using the
Collections.synchronizedList
method. This is best done at creation time, to prevent accidental
unsynchronized access to the list:
List list = Collections.synchronizedList(new ArrayList(...));
The iterators returned by this class's iterator and
listIterator methods are fail-fast:
if the list is structurally modified at any time after the iterator is
created, in any way except through the iterator's own
remove or
add methods, the iterator will throw a
ConcurrentModificationException. Thus, in the face of
concurrent modification, the iterator fails quickly and cleanly, rather
than risking arbitrary, non-deterministic behavior at an undetermined
time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.
This class is a member of the Java Collections Framework.
- Since:
- 1.2
- See Also:
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Field Summary
Fields declared in class java.util.AbstractList
modCount -
Constructor Summary
ConstructorsConstructorDescriptionConstructs an empty list with an initial capacity of ten.ArrayList(int initialCapacity) Constructs an empty list with the specified initial capacity.ArrayList(Collection<? extends E> c) Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. -
Method Summary
Modifier and TypeMethodDescriptionvoidInserts the specified element at the specified position in this list.booleanAppends the specified element to the end of this list.booleanaddAll(int index, Collection<? extends E> c) Inserts all of the elements in the specified collection into this list, starting at the specified position.booleanaddAll(Collection<? extends E> c) Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's Iterator.voidAdds an element as the first element of this collection (optional operation).voidAdds an element as the last element of this collection (optional operation).voidclear()Removes all of the elements from this list.clone()Returns a shallow copy of thisArrayListinstance.booleanReturnstrueif this list contains the specified element.voidensureCapacity(int minCapacity) Increases the capacity of thisArrayListinstance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.booleanCompares the specified object with this list for equality.voidPerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception.get(int index) Returns the element at the specified position in this list.getFirst()Gets the first element of this collection.getLast()Gets the last element of this collection.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.booleanisEmpty()Returnstrueif this list contains no elements.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.booleanRemoves the first occurrence of the specified element from this list, if it is present.booleanremoveAll(Collection<?> c) Removes from this list all of its elements that are contained in the specified collection.Removes and returns the first element of this collection (optional operation).booleanRemoves all of the elements of this collection that satisfy the given predicate.Removes and returns the last element of this collection (optional operation).protected voidremoveRange(int fromIndex, int toIndex) Removes from this list all of the elements whose index is betweenfromIndex, inclusive, andtoIndex, exclusive.booleanretainAll(Collection<?> c) Retains only the elements in this list that are contained in the specified collection.Replaces the element at the specified position in this list with the specified element.intsize()Returns the number of elements in this list.Creates a late-binding and fail-fastSpliteratorover the elements in this list.subList(int fromIndex, int toIndex) Returns a view of the portion of this list between the specifiedfromIndex, inclusive, andtoIndex, exclusive.Object[]toArray()Returns an array containing all of the elements in this list in proper sequence (from first to last element).<T> T[]toArray(T[] a) Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.voidTrims the capacity of thisArrayListinstance to be the list's current size.Methods declared in class java.util.AbstractList
equals, hashCodeMethods declared in class java.util.AbstractCollection
containsAll, toStringMethods declared in interface java.util.Collection
parallelStream, stream, toArrayMethods declared in interface java.util.List
containsAll, replaceAll, reversed, sort
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Constructor Details
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ArrayList
public ArrayList(int initialCapacity) Constructs an empty list with the specified initial capacity.- Parameters:
initialCapacity- the initial capacity of the list- Throws:
IllegalArgumentException- if the specified initial capacity is negative
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ArrayList
public ArrayList()Constructs an empty list with an initial capacity of ten. -
ArrayList
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.- Parameters:
c- the collection whose elements are to be placed into this list- Throws:
NullPointerException- if the specified collection is null
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Method Details
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trimToSize
public void trimToSize()Trims the capacity of thisArrayListinstance to be the list's current size. An application can use this operation to minimize the storage of anArrayListinstance. -
ensureCapacity
public void ensureCapacity(int minCapacity) Increases the capacity of thisArrayListinstance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.- Parameters:
minCapacity- the desired minimum capacity
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size
public int size()Returns the number of elements in this list. -
isEmpty
public boolean isEmpty()Returnstrueif this list contains no elements.- Specified by:
isEmptyin interfaceCollection<E>- Specified by:
isEmptyin interfaceList<E>- Overrides:
isEmptyin classAbstractCollection<E>- Returns:
trueif this list contains no elements
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contains
Returnstrueif this list contains the specified element. More formally, returnstrueif and only if this list contains at least one elementesuch thatObjects.equals(o, e).- Specified by:
containsin interfaceCollection<E>- Specified by:
containsin interfaceList<E>- Overrides:
containsin classAbstractCollection<E>- Parameters:
o- element whose presence in this list is to be tested- Returns:
trueif this list contains the specified element
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indexOf
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 indexisuch thatObjects.equals(o, get(i)), or -1 if there is no such index. -
lastIndexOf
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 indexisuch thatObjects.equals(o, get(i)), or -1 if there is no such index.- Specified by:
lastIndexOfin interfaceList<E>- Overrides:
lastIndexOfin classAbstractList<E>- 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
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clone
Returns a shallow copy of thisArrayListinstance. (The elements themselves are not copied.) -
toArray
Returns an array containing all of the elements in this list in proper sequence (from first to last element).The returned array will be "safe" in that no references to it are maintained by this list. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
- Specified by:
toArrayin interfaceCollection<E>- Specified by:
toArrayin interfaceList<E>- Overrides:
toArrayin classAbstractCollection<E>- Returns:
- an array containing all of the elements in this list in proper sequence
- See Also:
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toArray
public <T> T[] toArray(T[] a) Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list.If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the collection is set to
null. (This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.)- Specified by:
toArrayin interfaceCollection<E>- Specified by:
toArrayin interfaceList<E>- Overrides:
toArrayin classAbstractCollection<E>- Type Parameters:
T- the component type of the array to contain the collection- Parameters:
a- the array into which the elements of the list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.- Returns:
- an array containing the elements of the list
- Throws:
ArrayStoreException- if the runtime type of the specified array is not a supertype of the runtime type of every element in this listNullPointerException- if the specified array is null
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get
Returns the element at the specified position in this list.- Specified by:
getin interfaceList<E>- Specified by:
getin classAbstractList<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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getFirst
Gets the first element of this collection.- Specified by:
getFirstin interfaceList<E>- Specified by:
getFirstin interfaceSequencedCollection<E>- Returns:
- the retrieved element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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getLast
Gets the last element of this collection.- Specified by:
getLastin interfaceList<E>- Specified by:
getLastin interfaceSequencedCollection<E>- Returns:
- the retrieved element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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set
Replaces the element at the specified position in this list with the specified element.- Specified by:
setin interfaceList<E>- Overrides:
setin classAbstractList<E>- Parameters:
index- index of the element to replaceelement- element to be stored at the specified position- Returns:
- the element previously at the specified position
- Throws:
IndexOutOfBoundsException- if the index is out of range (index < 0 || index >= size())
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add
Appends the specified element to the end of this list.- Specified by:
addin interfaceCollection<E>- Specified by:
addin interfaceList<E>- Overrides:
addin classAbstractList<E>- Parameters:
e- element to be appended to this list- Returns:
true(as specified byCollection.add(E))
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add
Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).- Specified by:
addin interfaceList<E>- Overrides:
addin classAbstractList<E>- Parameters:
index- index at which the specified element is to be insertedelement- element to be inserted- Throws:
IndexOutOfBoundsException- if the index is out of range (index < 0 || index > size())
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addFirst
Adds an element as the first element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the first element in encounter order. -
addLast
Adds an element as the last element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the last element in encounter order. -
remove
Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).- Specified by:
removein interfaceList<E>- Overrides:
removein classAbstractList<E>- Parameters:
index- the index of the element to be removed- Returns:
- the element that was removed from the list
- Throws:
IndexOutOfBoundsException- if the index is out of range (index < 0 || index >= size())
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removeFirst
Removes and returns the first element of this collection (optional operation).- Specified by:
removeFirstin interfaceList<E>- Specified by:
removeFirstin interfaceSequencedCollection<E>- Returns:
- the removed element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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removeLast
Removes and returns the last element of this collection (optional operation).- Specified by:
removeLastin interfaceList<E>- Specified by:
removeLastin interfaceSequencedCollection<E>- Returns:
- the removed element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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equals
Compares 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 interfaceCollection<E>- Specified by:
equalsin interfaceList<E>- Overrides:
equalsin classAbstractList<E>- 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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hashCode
public int hashCode()Returns the hash code value for this list.- Specified by:
hashCodein interfaceCollection<E>- Specified by:
hashCodein interfaceList<E>- Overrides:
hashCodein classAbstractList<E>- Returns:
- the hash code value for this list
- See Also:
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remove
Removes the first occurrence of the specified element from this list, if it is present. If the list does not contain the element, it is unchanged. More formally, removes the element with the lowest indexisuch thatObjects.equals(o, get(i))(if such an element exists). Returnstrueif this list contained the specified element (or equivalently, if this list changed as a result of the call).- Specified by:
removein interfaceCollection<E>- Specified by:
removein interfaceList<E>- Overrides:
removein classAbstractCollection<E>- Parameters:
o- element to be removed from this list, if present- Returns:
trueif this list contained the specified element
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clear
public void clear()Removes all of the elements from this list. The list will be empty after this call returns.- Specified by:
clearin interfaceCollection<E>- Specified by:
clearin interfaceList<E>- Overrides:
clearin classAbstractList<E>
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addAll
Appends all of the elements in the specified collection to the end of 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. (This implies that the behavior of this call is undefined if the specified collection is this list, and this list is nonempty.)- Specified by:
addAllin interfaceCollection<E>- Specified by:
addAllin interfaceList<E>- Overrides:
addAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be added to this list- Returns:
trueif this list changed as a result of the call- Throws:
NullPointerException- if the specified collection is null- See Also:
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addAll
Inserts all of the elements in the specified collection into this list, starting at the specified position. 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.- Specified by:
addAllin interfaceList<E>- Overrides:
addAllin classAbstractList<E>- Parameters:
index- index at which to insert the first element from the specified collectionc- collection containing elements to be added to this list- Returns:
trueif this list changed as a result of the call- Throws:
IndexOutOfBoundsException- if the index is out of range (index < 0 || index > size())NullPointerException- if the specified collection is null
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removeRange
protected 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.)- Overrides:
removeRangein classAbstractList<E>- Parameters:
fromIndex- index of first element to be removedtoIndex- index after last element to be removed- Throws:
IndexOutOfBoundsException- iffromIndexortoIndexis out of range (fromIndex < 0 || toIndex > size() || toIndex < fromIndex)
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removeAll
Removes from this list all of its elements that are contained in the specified collection.- Specified by:
removeAllin interfaceCollection<E>- Specified by:
removeAllin interfaceList<E>- Overrides:
removeAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be removed from this list- Returns:
trueif this list changed as a result of the call- Throws:
ClassCastException- if the class of an element of this list is incompatible with the specified collection (optional)NullPointerException- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null- See Also:
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retainAll
Retains only the elements in this list that are contained in the specified collection. In other words, removes from this list all of its elements that are not contained in the specified collection.- Specified by:
retainAllin interfaceCollection<E>- Specified by:
retainAllin interfaceList<E>- Overrides:
retainAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be retained in this list- Returns:
trueif this list changed as a result of the call- Throws:
ClassCastException- if the class of an element of this list is incompatible with the specified collection (optional)NullPointerException- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null- See Also:
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listIterator
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 tonext. An initial call topreviouswould return the element with the specified index minus one.The returned list iterator is fail-fast.
- Specified by:
listIteratorin interfaceList<E>- Overrides:
listIteratorin classAbstractList<E>- 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())
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listIterator
Returns a list iterator over the elements in this list (in proper sequence).The returned list iterator is fail-fast.
- Specified by:
listIteratorin interfaceList<E>- Overrides:
listIteratorin classAbstractList<E>- Returns:
- a list iterator over the elements in this list (in proper sequence)
- See Also:
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iterator
Returns an iterator over the elements in this list in proper sequence.The returned iterator is fail-fast.
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subList
Returns 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.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 forindexOf(Object)andlastIndexOf(Object), 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 interfaceList<E>- Overrides:
subListin classAbstractList<E>- Parameters:
fromIndex- low endpoint (inclusive) of the subListtoIndex- 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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forEach
Description copied from interface:IterablePerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
- Specified by:
forEachin interfaceIterable<E>- Parameters:
action- The action to be performed for each element- Throws:
NullPointerException- if the specified action is null
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spliterator
Creates a late-binding and fail-fastSpliteratorover the elements in this list.The
SpliteratorreportsSpliterator.SIZED,Spliterator.SUBSIZED, andSpliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values.- Specified by:
spliteratorin interfaceCollection<E>- Specified by:
spliteratorin interfaceIterable<E>- Specified by:
spliteratorin interfaceList<E>- Returns:
- a
Spliteratorover the elements in this list - Since:
- 1.8
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removeIf
Description copied from interface:CollectionRemoves all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.- Specified by:
removeIfin interfaceCollection<E>- Parameters:
filter- a predicate which returnstruefor elements to be removed- Returns:
trueif any elements were removed- Throws:
NullPointerException- if the specified filter is null
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