Java-ArrayList class

• Java ArrayList class uses a dynamic array for storing the elements.It extends AbstractList class and implements List interface.
• ArrayList supports dynamic array which can grow as needed.
• Size of ArrayList can be dynamically increased or decreased.
• Java ArrayList class can contain duplicate elements.
• Java ArrayList class maintains insertion order of elements.
• Java ArrayList class is non synchronized.
• Java ArrayList allows random access because array works at the index basis.
•  Java ArrayList class, manipulation is slow because a lot of shifting needs to be occurred if any element is removed from the array list.

 

class ArrayList <T>

We can create ArrayList for storing String type elements as follows:

ArrayList <String> hs=new ArrayList <String> ();

We can create ArrayList for storing Integer type elements as follows:

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

 

 Constructors of ArrayList class as show below:

• ArrayList (): It builds an empty array list.
• ArrayList (Collection c): It builds an array list which is initialized with elements of the collection c.
• ArrayList (int capacity): It builds arraylist which has specified initial capacity .

 

Methods of ArrayList Class

Method	Description
void add(int position, element obj)	It inserts specified element at the specified position in the ArrayList.
boolean add(element obj)	It appends specified element to the end of the ArrayList.
boolean addAll(Collection c)	It appends all the elements of the collection to the end of the ArrayList.
element remove(int position)	It removes specified element at the specified position in the ArrayList.
boolean remove(object obj)	It removes first occurrence of specified element obj from the ArrayList.
void clear()	It removes all the elements from the ArrayList.
boolean contains(Object o)	It returns true if ArrayList contains the specified element .
object get(int position)	It returns the element at the specified position in the ArrayList.
int indexOf(Object o)	It returns first occurrence of the specified element in the list or -1 if element not found in the list.
int lastIndexOf(Object o)	It returns the last occurrence of the specified element in the list or -1 if the element is not found in the list.
int size()	It returns the number of elements in the list.

Example of java ArrayList class

     

import java.util.Iterator;

import java.util.ArrayList;

 

public class MyArrayList {

 

    public static void main(String a[]){

        ArrayList<String> al = new ArrayList<String>();

        //adding elements to the end

        al.add("A");

        al.add("B");

        al.add("C");

        al.add("D");

        Iterator<String> itr = al.iterator();

        while(itr.hasNext()){

            System.out.println(itr.next());

        }

    }

}

Output:

A
B
C
D

 Download this example from Here

Another example of java ArrayList class

import java.util.ArrayList;

 

public class MyArrayListOperation {

 

    public static void main(String[] a){

         

        ArrayList<String> al = new ArrayList<String>();

        //add elements to the ArrayList

        al.add("C");

        al.add("C++");

        al.add("java");

        al.add("PHP");

                 System.out.println("Size of the arraylist is: "+al.size());

        System.out.println(al);

        //get elements by index

        System.out.println("Element at index 1: "+al.get(2));

        //add elements at a specific index

        al.add(2,".Net");

        System.out.println(al);

        System.out.println("Is arraylist empty? "+al.isEmpty());

        System.out.println("Index of PERL is "+al.indexOf("Java"));

        

    }

}

Output:
Size of the arraylist is: 4

[C, C++, Java, PHP]
Element at index 2: Java
[C, C++,.Net ,Java, PHP]
Is arraylist empty? false
Index of Java is 3