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Java ArrayList Class

Java ArrayList Class Introduction

The Java ArrayList class provides resizable-array and implements the List interface.Following are the important points about ArrayList −

It implements all optional list operations and it also permits all elements, includes null.
It provides methods to manipulate the size of the array that is used internally to store the list.
The constant factor is low compared to that for the LinkedList implementation.

The ArrayList class extends AbstractList and implements the List interface. ArrayList supports dynamic arrays that can grow as needed.

Standard Java arrays are of a fixed length. After arrays are created, they cannot grow or shrink, which means that you must know in advance how many elements an array will hold.

Array lists are created with an initial size. When this size is exceeded, the collection is automatically enlarged. When objects are removed, the array may be shrunk.

Class declaration

Following is the declaration for java.util.ArrayList class −

public class ArrayList<E>
   extends AbstractList<E>
   implements Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess

Here <E> represents an Element. For example, if you're building an array list of Integers then you'd initialize it as

ArrayList<Integer> list = new ArrayList<Integer>();

Class constructors Sr.No. Constructor & Description 1

ArrayList()

This constructor is used to create an empty list with an initial capacity sufficient to hold 10 elements.

ArrayList(Collection<? extends E> c)

This constructor is used to create a list containing the elements of the specified collection.

ArrayList(int initialCapacity)

This constructor is used to create an empty list with an initial capacity.

Class methods Methods inherited

This class inherits methods from the following classes −

java.util.AbstractList
java.lang.AbstractCollection
java.util.Object
java.util.List

Adding, Removing Elements to ArrayList of Strings Example

The following program illustrates several of the methods supported by ArrayList −

package com.tutorialspoint;

import java.util.ArrayList;

public class ArrayListDemo {

   public static void main(String args[]) {
      // create an array list
      ArrayList al = new ArrayList();
      System.out.println("Initial size of al: " + al.size());

      // add elements to the array list
      al.add("C");
      al.add("A");
      al.add("E");
      al.add("B");
      al.add("D");
      al.add("F");
      al.add(1, "A2");
      System.out.println("Size of al after additions: " + al.size());

      // display the array list
      System.out.println("Contents of al: " + al);

      // Remove elements from the array list
      al.remove("F");
      al.remove(2);
      System.out.println("Size of al after deletions: " + al.size());
      System.out.println("Contents of al: " + al);
   }
}

This will produce the following result −

Output

Initial size of al: 0
Size of al after additions: 7
Contents of al: [C, A2, A, E, B, D, F]
Size of al after deletions: 5
Contents of al: [C, A2, E, B, D]

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