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 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 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.
Field Detail |
private transient java.lang.Object[] elementData
private int size
Constructor Detail |
public ArrayList(int initialCapacity)
initialCapacity
- the initial capacity of the list.IllegalArgumentException
- if the specified initial capacity is negativepublic ArrayList()
public ArrayList(java.util.Collection c)
c
- the collection whose elements are to be placed into this list.NullPointerException
- if the specified collection is null.Method Detail |
public void trimToSize()
public void ensureCapacity(int minCapacity)
minCapacity
- the desired minimum capacity.public int size()
public boolean isEmpty()
public boolean contains(java.lang.Object elem)
elem
- element whose presence in this List is to be tested.true
if the specified element is present; false
otherwise.public int indexOf(java.lang.Object elem)
elem
- an object.public int lastIndexOf(java.lang.Object elem)
elem
- the desired element.public java.lang.Object clone()
public java.lang.Object[] toArray()
public java.lang.Object[] toArray(java.lang.Object[] a)
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.
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.ArrayStoreException
- if the runtime type of a is not a supertype of the runtime type of every element in this list.public java.lang.Object get(int index)
index
- index of element to return.IndexOutOfBoundsException
- if index is out of range (index < 0 || index >= size()).public java.lang.Object set(int index, java.lang.Object element)
index
- index of element to replace.element
- element to be stored at the specified position.IndexOutOfBoundsException
- if index out of range (index < 0 || index >= size()).public boolean add(java.lang.Object o)
o
- element to be appended to this list.public void add(int index, java.lang.Object element)
index
- index at which the specified element is to be inserted.element
- element to be inserted.IndexOutOfBoundsException
- if index is out of range (index < 0 || index > size()).public java.lang.Object remove(int index)
index
- the index of the element to removed.IndexOutOfBoundsException
- if index out of range (index < 0 || index >= size()).public void clear()
public boolean addAll(java.util.Collection c)
c
- the elements to be inserted into this list.IndexOutOfBoundsException
- if index out of range (index < 0 || index > size()).NullPointerException
- if the specified collection is null.public boolean addAll(int index, java.util.Collection c)
index
- index at which to insert first element from the specified collection.c
- elements to be inserted into this list.IndexOutOfBoundsException
- if index out of range (index < 0 || index > size()).NullPointerException
- if the specified Collection is null.protected void removeRange(int fromIndex, int toIndex)
fromIndex
- index of first element to be removed.toIndex
- index after last element to be removed.private void RangeCheck(int index)
private synchronized void writeObject(java.io.ObjectOutputStream s)
private synchronized void readObject(java.io.ObjectInputStream s)