What is arraylist in java

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. 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. ArrayList int initialCapacity Constructs an empty list with the specified initial capacity.

Object clone Returns a shallow copy of this ArrayList instance. E get int index Returns the element at the specified position in this list. E remove int index Removes the element at the specified position in this list. E set int index, E element Replaces the element at the specified position in this list with the specified element.

Object [] toArray Returns an array containing all of the elements in this list in proper sequence from first to last element. Methods inherited from class java. AbstractList equals , hashCode Methods inherited from class java. AbstractCollection containsAll , toString Methods inherited from class java. Object finalize , getClass , notify , notifyAll , wait , wait , wait Methods inherited from interface java. List containsAll , equals , hashCode Methods inherited from interface java.

Parameters: initialCapacity - the initial capacity of the list Throws: IllegalArgumentException - if the specified initial capacity is negative ArrayList public ArrayList Constructs an empty list with an initial capacity of ten. Parameters: c - the collection whose elements are to be placed into this list Throws: NullPointerException - if the specified collection is null Method Detail trimToSize 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. Parameters: minCapacity - the desired minimum capacity size public int size Returns the number of elements in this list.

The elements themselves are not copied. Overrides: clone in class Object Returns: a clone of this ArrayList instance See Also: Cloneable toArray 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. It inherits the AbstractList class and implements List interface. The important points about Java ArrayList class are:. The List interface extends the Collection and Iterable interfaces in hierarchical order. Java new generic collection allows you to have only one type of object in a collection.

Now it is type safe so typecasting is not required at runtime. In a generic collection, we specify the type in angular braces. Now ArrayList is forced to have the only specified type of objects in it. If you try to add another type of object, it gives compile time error. For more information on Java generics, click here Java Generics Tutorial.

Java ArrayList Example import java. The get method returns the element at the specified index, whereas the set method changes the element. The java. Using the Collections. Difference between ArrayList and LinkedList. Difference between length of array and size of ArrayList in Java. How to remove duplicates from ArrayList in Java. JavaTpoint offers too many high quality services. We just launched W3Schools videos. Get certified by completing a course today! If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:.

Example Create an ArrayList object called cars that will store strings: import java. Example import java. Example cars. Example Create an ArrayList to store numbers add elements of type Integer : import java.

Example Sort an ArrayList of Strings: import java. ArrayList; import java. Example Sort an ArrayList of Integers: import java. ArrayList is a dynamic data structure in which you can add or remove any number of elements and those elements are stored in ordered sequence. It may also contain duplicate values.

ArrayList are the implementations of List interface. The package you required to import the ArrayList is import java. Important Note: In ArrayList, the items to be added are only of object type.