ArrayList

 

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

 

• Resizable-array implementation of the List interface. An ArrayList is used to store an "ordered" group of elements where duplicates are allowed.
• Implements all optional list operations, and permits all elements, including null.
• This class is similar to Vector, except that it is unsynchronized.
• The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. ArrayList's give great performance on get() and set() methods, but do not perform well on add() and remove() methods when compared to a LinkedList.
• An ArrayList capacity is the size of the array used to store the elements in the list. As elements are added to an ArrayList, its capacity grows automatically. It is an Array based implementation where elements of the List can be accessed directly through get() method.
  
  To prevent unsynchronized access to the list: List list = Collections.synchronizedList(new ArrayList(...));
   

Below is an ArrayList Example showing how collections are manipulated using an ArrayList

import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.Collections;
import java.util.Random;

public class ArrayListExample {


    public static void main(String[] args) {

//        ArrayList Creation
        List arraylistA = new ArrayList();
        List arraylistB = new ArrayList();

//        Adding elements to the ArrayList
        for (int i = 0; i < 5; i++) {
            arraylistA.add(new Integer(i));
        }

        arraylistB.add("beginner");
        arraylistB.add("java");
        arraylistB.add("tutorial");
        arraylistB.add(".");
        arraylistB.add("com");
        arraylistB.add("java");
        arraylistB.add("site");
        
//      Iterating through the ArrayList to display the Contents. 
        Iterator i1 = arraylistA.iterator();
        System.out.print("ArrayList arraylistA --> ");
        while (i1.hasNext()) {
            System.out.print(i1.next()+ " , ");
        }
        System.out.println();
        System.out.print("ArrayList arraylistA --> ");
        for (int j=0; j < arraylistA.size(); j++) {
            System.out.print(arraylistA.get(j)+ " , ");
        }
        System.out.println();
        Iterator i2 = arraylistB.iterator();
        System.out.println("ArrayList arraylistB --> ");
        while (i2.hasNext()) {
            System.out.print(i2.next()+ " , ");
        }
        
        System.out.println();
        System.out.println();
        System.out.println("Using ListIterator to retrieve ArrayList Elements");
        System.out.println();

        ListIterator li1 = arraylistA.listIterator();
//       next(), hasPrevious(), hasNext(), hasNext() nextIndex() can be used with a 
//        ListIterator interface implementation
        System.out.println("ArrayList arraylistA --> ");
        while (li1.hasNext()) {
        	System.out.print(li1.next()+ " , ");
        }

        System.out.println();
        
//        Searching for an element in the ArrayList
        int index = arraylistB.indexOf("java");
        System.out.println("'java' was found at : " + index); 
        int lastIndex = arraylistB.lastIndexOf("java");
        System.out.println("'java' was found at : " + lastIndex+" from the last");
        System.out.println();
        
//        Getting the subList from the original List
        List subList = arraylistA.subList(3, arraylistA.size());
        System.out.println("New Sub-List(arraylistA) from index 3 to " 
        				+ arraylistA.size() + ": " + subList);
        System.out.println();
        
//        Sort an ArrayList
        System.out.print("Sorted ArrayList arraylistA --> ");
        Collections.sort(arraylistA);
        System.out.print(arraylistA);
        System.out.println();

//      Reversing an ArrayList
        System.out.print("Reversed ArrayList arraylistA --> ");
        Collections.reverse(arraylistA);
        System.out.println(arraylistA);
        System.out.println();
        
//		Checking emptyness of an ArrayList
        System.out.println("Is arraylistA empty?   " + arraylistA.isEmpty());
        System.out.println();

//        Checking for Equality of ArrayLists
        ArrayList arraylistC = new ArrayList(arraylistA);
        System.out.println("arraylistA.equals(arraylistC)? " 

						+ arraylistA.equals(arraylistC));
        System.out.println();

//      Shuffling the elements of an ArrayList in Random Order
        Collections.shuffle(arraylistA, new Random());
        System.out.print("ArrayList arraylistA after shuffling its elements--> ");
        i1 = arraylistA.iterator();
        while (i1.hasNext()) {
            System.out.print(i1.next()+ " , ");
        }
        System.out.println();
        System.out.println();
//        Converting an ArrayList to an Array
        Object[] array = arraylistA.toArray();
        for (int i=0; i < array.length; i++) {
            System.out.println("Array Element [" + i + "] = " + array[i]);
        }
        System.out.println();

//        Clearing ArrayList Elements
        arraylistA.clear();
        System.out.println("arraylistA after clearing  : " + arraylistA);
        System.out.println();
    }

}

     

Output

ArrayList arraylistA --> 0 , 1 , 2 , 3 , 4 ,
ArrayList arraylistA --> 0 , 1 , 2 , 3 , 4 ,
ArrayList arraylistB -->
beginner , java , tutorial , . , com , java , site ,

Using ListIterator to retrieve ArrayList Elements

ArrayList arraylistA -->
0 , 1 , 2 , 3 , 4 ,
'java' was found at : 1
'java' was found at : 5 from the last

New Sub-List(arraylistA) from index 3 to 5: [3, 4]

Sorted ArrayList arraylistA --> [0, 1, 2, 3, 4]
Reversed ArrayList arraylistA --> [4, 3, 2, 1, 0]

Is arraylistA empty? false

arraylistA.equals(arraylistC)? true

ArrayList arraylistA after shuffling its elements--> 3 , 2 , 1 , 0 , 4 ,

Array Element [0] = 3
Array Element [1] = 2
Array Element [2] = 1
Array Element [3] = 0
Array Element [4] = 4

arraylistA after clearing : []
 

Download ArrayListExample.java