Array List in Java

In this article you will learn about the Array Lists in Java and various Array List methods in Java.

Introduction

Array Lists are part of the List interface in Java. They are very important because of the reason that they can grow or shrink easily depending on the need. So if we do not know the size of our data then it is better to use an Array List. They are not restricted by size.

Array List

  • Array List is based on an array but different in the manner that it is resizable accordingly, unlike an array.
     
  • Array List is not synchronized.
     
  • Array List can grow or shrink accordingly.
     
  • Array List is the part of the List interface in Java.
     
  • Array List is synchronized; that is why they are not thread safe.
     
  • Array List also allows null values.

Array List Methods

There are various methods. We will explain some of them.

Creation of Array List

ArrayList <List_name> = new ArrayList();

Example

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        System.out.println("ArrayList is : " + ar);

    }

}


Output

creation of arraylist

 

Adding items into Array List

<List_name>.add("item");

Example

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        System.out.println("ArrayList is : " + ar);

    }

}

 

Output

adding item into arraylist

 


Finding size of Array List

<List_name>.size( );

Example
 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        System.out.println("ArrayList is : " + ar);

        System.out.println("Size of ArrayList is : " + ar.size());

    }

}


Output

size of arraylist

 

Retrieving item from Array List

<List_name>.get(index);

Example
 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        System.out.println("ArrayList is : " + ar);

        for (int i = 0; i < ar.size(); i++)

        {

            System.out.println("At index : " + i +" item is " + ar.get(i));

        }   

    }

}

Output

retrieving item from arraylist


Removing item from Array List

 

<List_name>.remove(index);

Or:

<List_name>.remove("item");

 

Example

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        ar.add("sam");

        System.out.println("ArrayList is : " + ar);

        ar.remove(1);

        System.out.println("New ArrayList is " + ar);

    }

}

 

Or:

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        ar.add("sam");

        System.out.println("ArrayList is : " + ar);

        ar.remove("ram");

        System.out.println("New ArrayList is " + ar);

    }

}

 

Output

removing item from arraylist

Removing all data from Array List

 

<List_name>.clear( );

 

Example

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        ar.add("sam");

        System.out.println("ArrayList is : " + ar);

        ar.clear();

        System.out.println("ArrayList is : " + ar);

    }

}

 

Output

clearing data from arraylist


Checking Array List

 

<List_name>.contains("item");

 

Example

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        ar.add("sam");

        System.out.println("ArrayList is : " + ar);

        boolean b = ar.contains("ram");

        System.out.println(b);

    }

}

 

Output

checking arraylist

 

Finding index of an item in Array List

 

<List_name>.indexOf("item");

 

Example

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        ar.add("sam");

        System.out.println("ArrayList is : " + ar);

        System.out.println("Index of ram is : " + ar.indexOf("ram"));

    }

}

 

Output

finding index of item


Checking for empty Array List

 

if(<List_name>.size() == 0)

        {

            System.out.println("Empty Array List");

        }

 

Example

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        if(ar.size() == 0)

        {

            System.out.println("Empty Array List");

        }

    }

}

 

Output

empty array list


Replacing item in Array List

 

<List_name>.set(index, "new item");

 

Example

 

package demo;

import java.util.*;

public class Demo

{

    public static void main(String args[])

    {

        ArrayList ar = new ArrayList();

        ar.add("raj");

        ar.add("ram");

        ar.add("sam");

        System.out.println("ArrayList is : " + ar);

        ar.set(1, "rambo");

        System.out.println("ArrayList is : " + ar);

    }

}

 

Output

replacing item from arraylist


Summary

 

This article explains the Array List in Java and various Array List methods in Java.