Class: java.util.ArrayList<E>
- 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 java.util.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.
Inheritance
Superclass tree:- java.lang.Object
- java.util.AbstractCollection<E>
- java.util.AbstractList<E>
- java.util.ArrayList
- RandomAccess
- Cloneable
- Serializable
- List<E>
- Collection<E>
- Iterable<E>
Methods
-
ArrayListtop
public ArrayList()Constructs an empty list with an initial capacity of ten. -
ArrayListtop
public ArrayList(int initialCapacity)Constructs an empty list with the specified initial capacity. -
ArrayListtop
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. -
addtop
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).- Override hierarchy:
- add from AbstractList<E>
-
addtop
public boolean add(E e)Appends the specified element to the end of this list.- Specified by:
- add from List<E>
- add from Collection<E>
- Override hierarchy:
- add from AbstractList<E>
- add from AbstractCollection<E>
-
addAlltop
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.- Override hierarchy:
- addAll from AbstractList<E>
-
addAlltop
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.)- Specified by:
- addAll from List<E>
- addAll from Collection<E>
- Override hierarchy:
- addAll from AbstractCollection<E>
-
batchRemovetop
private boolean batchRemove(Collection<?> c, boolean complement) -
cleartop
public void clear()Removes all of the elements from this list. The list will be empty after this call returns.- Specified by:
- clear from List<E>
- clear from Collection<E>
- Override hierarchy:
- clear from AbstractList<E>
- clear from AbstractCollection<E>
-
clonetop
public Object clone()Returns a shallow copy of this ArrayList instance. (The elements themselves are not copied.) -
containstop
public 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)).- Specified by:
- contains from List<E>
- contains from Collection<E>
- Override hierarchy:
- contains from AbstractCollection<E>
-
elementDatatop
E elementData(int index)- @SuppressWarnings(value={"unchecked"})
-
ensureCapacitytop
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. -
fastRemovetop
private void fastRemove(int index) -
gettop
public E get(int index)Returns the element at the specified position in this list.- Override hierarchy:
- get from AbstractList<E>
-
indexOftop
public 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.- Override hierarchy:
- indexOf from AbstractList<E>
-
isEmptytop
public boolean isEmpty()Returns true if this list contains no elements.- Specified by:
- isEmpty from List<E>
- isEmpty from Collection<E>
- Override hierarchy:
- isEmpty from AbstractCollection<E>
-
iteratortop
public Iterator<E> iterator()Returns an iterator over the elements in this list in proper sequence.The returned iterator is fail-fast.
- Override hierarchy:
- iterator from AbstractList<E>
- iterator from AbstractCollection<E>
-
lastIndexOftop
public 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.- Specified by:
- lastIndexOf from List<E>
- Override hierarchy:
- lastIndexOf from AbstractList<E>
-
listIteratortop
public ListIterator<E> listIterator()Returns a list iterator over the elements in this list (in proper sequence).The returned list iterator is fail-fast.
- Specified by:
- listIterator from List<E>
- Override hierarchy:
- listIterator from AbstractList<E>
-
listIteratortop
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.
- Specified by:
- listIterator from List<E>
- Override hierarchy:
- listIterator from AbstractList<E>
-
outOfBoundsMsgtop
private String outOfBoundsMsg(int index)Constructs an IndexOutOfBoundsException detail message. Of the many possible refactorings of the error handling code, this "outlining" performs best with both server and client VMs.- Override hierarchy:
- outOfBoundsMsg from AbstractList<E>
-
rangeChecktop
private void rangeCheck(int index)Checks if the given index is in range. If not, throws an appropriate runtime exception. This method does *not* check if the index is negative: It is always used immediately prior to an array access, which throws an ArrayIndexOutOfBoundsException if index is negative. -
rangeCheckForAddtop
private void rangeCheckForAdd(int index)A version of rangeCheck used by add and addAll.- Override hierarchy:
- rangeCheckForAdd from AbstractList<E>
-
readObjecttop
private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundExceptionReconstitute the ArrayList instance from a stream (that is, deserialize it). -
removetop
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).- Override hierarchy:
- remove from AbstractList<E>
-
removetop
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).- Specified by:
- remove from List<E>
- remove from Collection<E>
- Override hierarchy:
- remove from AbstractCollection<E>
-
removeAlltop
public boolean removeAll(Collection<?> c)Removes from this list all of its elements that are contained in the specified collection.- Specified by:
- removeAll from List<E>
- removeAll from Collection<E>
- Override hierarchy:
- removeAll from AbstractCollection<E>
-
removeRangetop
protected 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.)- Override hierarchy:
- removeRange from AbstractList<E>
-
retainAlltop
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.- Specified by:
- retainAll from List<E>
- retainAll from Collection<E>
- Override hierarchy:
- retainAll from AbstractCollection<E>
-
settop
public E set(int index, E element)Replaces the element at the specified position in this list with the specified element.- Override hierarchy:
- set from AbstractList<E>
-
sizetop
public int size()Returns the number of elements in this list.- Specified by:
- size from List<E>
- size from Collection<E>
- Override hierarchy:
- size from AbstractCollection<E>
-
subListtop
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 java.util.ArrayList.indexOf(java.lang.Object) and java.util.ArrayList.lastIndexOf(java.lang.Object), and all of the algorithms in the java.util.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.)
- Override hierarchy:
- subList from AbstractList<E>
-
subListRangeChecktop
static void subListRangeCheck(int fromIndex, int toIndex, int size) -
toArraytop
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.
- Specified by:
- toArray from List<E>
- toArray from Collection<E>
- Override hierarchy:
- toArray from AbstractCollection<E>
-
toArraytop
public <T> T[] toArray(T[] a)- @SuppressWarnings(value={"unchecked"})
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:
- toArray from List<E>
- toArray from Collection<E>
- Override hierarchy:
- toArray from AbstractCollection<E>
-
trimToSizetop
public 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. -
writeObjecttop
private void writeObject(ObjectOutputStream s) throws IOExceptionSave the state of the ArrayList instance to a stream (that is, serialize it).
Fields
-
elementData
transient private Object[] elementDataThe array buffer into which the elements of the ArrayList are stored. The capacity of the ArrayList is the length of this array buffer. -
serialVersionUID
static final private long serialVersionUID = 8683452581122892189 -
size
private int sizeThe size of the ArrayList (the number of elements it contains).