- The ArrayList class in Java extends AbstractList and implements List Interface and also allows null.
- The ArrayList class is a dynamic array that can grow and shrink at runtime.
- ArrayList class is expandable or re – sizable array and used behalf of array because array is fixed size and cannot modify once we create it.
- ArrayList allows duplicate elements.
- ArrayList support both Iterator and ListIterator for iteration purpose.
- ArrayList is not synchronized and hence it not thread safe.
- ArrayList support single dimensional and heterogeneous data.
The following table demonstrates the constructors of the ArrayList class and its methods.
Constructor | Meaning |
ArrayList | Constructs an Empty ArrayList Object. |
ArrayList(Collection c) | Constructs a list containing the elements of the given collection. |
ArrayList(int capacity) | Constructs an ArrayList object with the given initial capacity. |
The following program shows a simple use of ArrayList. An array list is created, and then objects of type String are added to it. The list is then displayed.
Example:
/**
From SimpleArrayList.java
*/
import java.util.ArrayList;
/**
*
* @author JavaHotSpot
*/
public class SimpleArrayList
{
public static void main(String args[])
{
ArrayList alist = new ArrayList();
alist.add("Book1");
alist.add("Book2");
alist.add("Book3");
alist.add("Book4");
alist.add("Book5");
alist.add("Book6");
alist.add("Book7");
System.out.println("The size of the ArrayList="+alist.size());
System.out.println("The elements of ArrayList are..."+"\n"+alist);
alist.remove("Book7");
System.out.println("The size of the ArrayList after removing single item="+alist.size());
System.out.println("The elements of ArrayList are..."+"\n"+alist);
}
}
Output:
The size of the ArrayList=7
The elements of ArrayList are...
[Book1, Book2, Book3, Book4, Book5, Book6, Book7]
The size of the ArrayList after removing single item=6
The elements of ArrayList are...
[Book1, Book2, Book3, Book4, Book5, Book6]