Array List 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

 

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

 

Finding the 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

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

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 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

 

 

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

 

 

Finding an 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

 

 

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

 

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

 

 

Summary

 

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