ArrayList in Java Collections Framework

public class ArrayList

extends AbstractList

implements List, 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 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.

Constructor Details

 

1) 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

2) public ArrayList()

Constructs an empty list with an initial capacity of ten.

3) public ArrayList(Collection c)

Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. The ArrayList instance has an initial capacity of 110% the size of the specified collection.

Parameters:

c - the collection whose elements are to be placed into this list.

Throws:

NullPointerException - if the specified collection is null.

Method Details

In addition to the methods inherited from the List interface the ArrayList class contains some new methods.Let us discuss about some of them.


1) 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.

2) 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.

                Parameters:
                         minCapacity - the desired minimum capacity.

3) 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.)

             Overrides:
                       removeRange in class AbstractList
           Parameters:
                       fromIndex - index of first element to be removed.
                       toIndex - index after last element to be removed.


The links you may like:

Collection Interface in Java

List Interface in Java