public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, Serializable
Resizable-array implementation of the 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.
Collection, List, LinkedList, Vector, Serialized FormmodCount public ArrayList(int initialCapacity)
Constructs an empty list with the specified initial capacity.
initialCapacity - the initial capacity of the listIllegalArgumentException - if the specified initial capacity is negativepublic ArrayList()
Constructs an empty list with an initial capacity of ten.
public 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.
c - the collection whose elements are to be placed into this listNullPointerException - if the specified collection is nullpublic void trimToSize()
Trims the capacity of this ArrayList instance to be the list's current size. An application can use this operation to minimize the storage of an ArrayList instance.
public void ensureCapacity(int minCapacity)
Increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.
minCapacity - the desired minimum capacitypublic int size()
Returns the number of elements in this list.
size in interface Collection<E>
size in interface List<E>
size in class AbstractCollection<E>
public boolean isEmpty()
Returns true if this list contains no elements.
isEmpty in interface Collection<E>
isEmpty in interface List<E>
isEmpty in class AbstractCollection<E>
true if this list contains no elementspublic boolean contains(Object o)
Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).
contains in interface Collection<E>
contains in interface List<E>
contains in class AbstractCollection<E>
o - element whose presence in this list is to be testedtrue if this list contains the specified elementpublic int indexOf(Object o)
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 index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
indexOf in interface List<E>
indexOf in class AbstractList<E>
o - element to search forpublic int lastIndexOf(Object o)
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 index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
lastIndexOf in interface List<E>
lastIndexOf in class AbstractList<E>
o - element to search forpublic Object clone()
Returns a shallow copy of this ArrayList instance. (The elements themselves are not copied.)
public Object[] 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.
toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
Arrays.asList(Object[])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.)
toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
T - the runtime type of the array to contain the collectiona - 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.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 nullpublic E get(int index)
Returns the element at the specified position in this list.
get in interface List<E>
get in class AbstractList<E>
index - index of the element to returnIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())public E set(int index,
E element) Replaces the element at the specified position in this list with the specified element.
set in interface List<E>
set in class AbstractList<E>
index - index of the element to replaceelement - element to be stored at the specified positionIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())public boolean add(E e)
Appends the specified element to the end of this list.
add in interface Collection<E>
add in interface List<E>
add in class AbstractList<E>
e - element to be appended to this listtrue (as specified by Collection.add(E))public void add(int index,
E element) 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).
add in interface List<E>
add in class AbstractList<E>
index - index at which the specified element is to be insertedelement - element to be insertedIndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())public E remove(int index)
Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).
remove in interface List<E>
remove in class AbstractList<E>
index - the index of the element to be removedIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())public boolean remove(Object o)
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 index i such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).
remove in interface Collection<E>
remove in interface List<E>
remove in class AbstractCollection<E>
o - element to be removed from this list, if presenttrue if this list contained the specified elementpublic void clear()
Removes all of the elements from this list. The list will be empty after this call returns.
clear in interface Collection<E>
clear in interface List<E>
clear in class AbstractList<E>
public boolean addAll(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. 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.)
addAll in interface Collection<E>
addAll in interface List<E>
addAll in class AbstractCollection<E>
c - collection containing elements to be added to this listtrue if this list changed as a result of the callNullPointerException - if the specified collection is nullAbstractCollection.add(Object)public boolean addAll(int index,
Collection<? extends E> c) 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.
addAll in interface List<E>
addAll in class AbstractList<E>
index - index at which to insert the first element from the specified collectionc - collection containing elements to be added to this listtrue if this list changed as a result of the callIndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())NullPointerException - if the specified collection is nullprotected void removeRange(int fromIndex,
int toIndex) 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 list by (toIndex - fromIndex) elements. (If toIndex==fromIndex, this operation has no effect.)
removeRange in class AbstractList<E>
fromIndex - index of first element to be removedtoIndex - index after last element to be removedIndexOutOfBoundsException - if fromIndex or toIndex is out of range (fromIndex < 0 ||
fromIndex >= size() ||
toIndex > size() ||
toIndex < fromIndex)public boolean removeAll(Collection<?> c)
Removes from this list all of its elements that are contained in the specified collection.
removeAll in interface Collection<E>
removeAll in interface List<E>
removeAll in class AbstractCollection<E>
c - collection containing elements to be removed from this listtrue if this list changed as a result of the callClassCastException - 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 nullCollection.contains(Object)public boolean retainAll(Collection<?> c)
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.
retainAll in interface Collection<E>
retainAll in interface List<E>
retainAll in class AbstractCollection<E>
c - collection containing elements to be retained in this listtrue if this list changed as a result of the callClassCastException - 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 nullCollection.contains(Object)public ListIterator<E> listIterator(int index)
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 to next. An initial call to previous would return the element with the specified index minus one.
The returned list iterator is fail-fast.
listIterator in interface List<E>
listIterator in class AbstractList<E>
index - index of the first element to be returned from the list iterator (by a call to next)IndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())public ListIterator<E> listIterator()
Returns a list iterator over the elements in this list (in proper sequence).
The returned list iterator is fail-fast.
listIterator in interface List<E>
listIterator in class AbstractList<E>
listIterator(int)public Iterator<E> iterator()
Returns an iterator over the elements in this list in proper sequence.
The returned iterator is fail-fast.
iterator in interface Iterable<E>
iterator in interface Collection<E>
iterator in interface List<E>
iterator in class AbstractList<E>
public List<E> subList(int fromIndex,
int toIndex) Returns a view of the portion of this list between the specified 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 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 for
indexOf(Object) and lastIndexOf(Object), 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 this list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)
subList in interface List<E>
subList in class AbstractList<E>
fromIndex - low endpoint (inclusive) of the subListtoIndex - high endpoint (exclusive) of the subListIndexOutOfBoundsException - if an endpoint index value is out of range (fromIndex < 0 || toIndex > size)
IllegalArgumentException - if the endpoint indices are out of order (fromIndex > toIndex)
public void forEach(Consumer<? super E> action)
Description copied from interface: Iterable
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. Unless otherwise specified by the implementing class, actions are performed in the order of iteration (if an iteration order is specified). Exceptions thrown by the action are relayed to the caller.
forEach in interface Iterable<E>
action - The action to be performed for each elementpublic Spliterator<E> spliterator()
Creates a late-binding and fail-fast Spliterator over the elements in this list.
The Spliterator reports Spliterator.SIZED, Spliterator.SUBSIZED, and Spliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values.
spliterator in interface Iterable<E>
spliterator in interface Collection<E>
spliterator in interface List<E>
Spliterator over the elements in this listpublic boolean removeIf(Predicate<? super E> filter)
Description copied from interface: Collection
Removes 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.
removeIf in interface Collection<E>
filter - a predicate which returns true for elements to be removedtrue if any elements were removedpublic void replaceAll(UnaryOperator<E> operator)
Description copied from interface: List
Replaces each element of this list with the result of applying the operator to that element. Errors or runtime exceptions thrown by the operator are relayed to the caller.
replaceAll in interface List<E>
operator - the operator to apply to each elementpublic void sort(Comparator<? super E> c)
Description copied from interface: List
Sorts this list according to the order induced by the specified Comparator.
All elements in this list must be mutually comparable using the specified comparator (that is, c.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the list).
If the specified comparator is null then all elements in this list must implement the Comparable interface and the elements' natural ordering should be used.
This list must be modifiable, but need not be resizable.
sort in interface List<E>
c - the Comparator used to compare list elements. A null value indicates that the elements' natural ordering should be used
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