Differences Between Array and ArrayList in Java

Last Updated : 13 Jan 2026

In Java, array and ArrayLists are well-known data structures. An array is a basic functionality provided by Java, whereas an ArrayList is a class of the Java Collections framework. It belongs to java.util package.

Java Array

An array is a dynamically created object. It serves as a container that holds a constant number of values of the same type. It has a contiguous memory location. Once an array is created, we cannot change its size. We can create an array by using the following statement:

The above statement creates an array of the specified size. When we try to add more than its size, it throws an ArrayIndexOutOfBoundsException. For example:

int arr[]=new int[3];   //specified size of array is 3  
//adding four elements into an array   
arr[0]=12;  
arr[1]=2;  
arr[2]=15;  
arr[3]=67;  

To read more Java Array

Example of an Array

In the following example, we have simply created an array of length four.

Example

public class Main{  
public static void main(String args[])  {  
//creating an array of integer type   
int arr[]=new int[4];  
//adding elements into an array   
arr[0]=12;  
arr[1]=2;  
arr[2]=15;  
arr[3]=67;  
for(int i=0;i<arr.length;i++)  {  
System.out.println(arr[i]);  
}  
}  
}  

Compile and Run

Output:

Java ArrayList Class

In Java, ArrayList is a class of the Collections framework. It implements List<E>, Collection<E>, Iterable<E>, Cloneable, Serializable, and RandomAccess interfaces. It extends the AbstractList<E> class.

We can create an instance of ArrayList by using the following statement:

An array in Java internally backs an ArrayList. The resize operation in ArrayList slows down the performance as it involves a new array and copying content from the old array to the new array. It calls the native implemented method System.arraycopy(sec, srcPos, dest, destPos, length).

We cannot store a primitive type in an ArrayList. So, it stores only objects. It automatically converts a primitive type to an object. For example, we have created an ArrayList object,

ArrayList <Integer> list=new ArrayList<Integer>();  //object of ArrayList  
arrayObj.add(12);   //trying to add an integer primitive to the ArrayList  

The JVM converts it into an Integer object through auto-boxing.

ArrayList arrayObj=new ArrayList()//object of ArrayList  
arrayObj(new Integer(12)); //converts integer primitive to Integer object and adds to ArrayList object  

To read more Java ArrayList

Example of ArrayList

In the following example, we have created an instance of ArrayList and are performing iteration over the ArrayList.

Example

import java.util.*;  
public class Main{   
public static void main(String args[])   {   
//creating an instance of ArrayList  
List<Float> list = new ArrayList<Float>();   
//adding element to ArrayList  
list.add(12.4f);   
list.add(34.6f);   
list.add(56.8f);   
list.add(78.9f);   
//iteration over ArrayList using for-each loop  
for(Float f:list)  {  
System.out.println(f);   
}  
}   
}  

Compile and Run

Output:

12.4
34.6
56.8
78.9

Similarities

Array and ArrayList both are used for storing elements.
Array and ArrayList both can store null values.
They can have duplicate values.
They generally preserve the order of elements.

Array Vs. ArrayList

The following table describes the key differences between an array and an ArrayList:

Basis	Array	ArrayList
Definition	An array is a dynamically created object. It serves as a container that holds a constant number of values of the same type. It has a contiguous memory location.	The ArrayList is a class of the Java Collections framework. It contains popular classes like Vector, HashTable, and HashMap.
Static/ Dynamic	An array is static in size.	ArrayList is dynamic in size.
Resizable	An array is a fixed-length data structure.	ArrayList is a variable-length data structure. It can be resized itself when needed.
Initialization	It is mandatory to provide the size of an array while initializing it directly or indirectly.	We can create an instance of ArrayList without specifying its size. Java creates an ArrayList of default size.
Performance	It performs fast in comparison to ArrayList because of its fixed size.	An array in Java internally backs an ArrayList. The resize operation in ArrayList slows down the performance.
Primitive/ Generic type	An array can store both object and primitive types.	We cannot store a primitive type in an ArrayList. It automatically converts a primitive type to an object.
Iterating Values	We use a for loop or a foreach loop to iterate over an array.	We use an iterator to iterate over an ArrayList.
Type-Safety	We cannot use generics along with an array because it is not a convertible type of array.	ArrayList allows us to store only generic/ type, so it is type-safe.
Length	Array provides a length variable that denotes the length of an array.	ArrayList provides the size() method to determine the size of the ArrayList.
Adding Elements	We can add elements to an array by using the assignment operator.	Java provides the add() method to add elements to the ArrayList.
Single/ Multi-Dimensional	An array can be multi-dimensional.	ArrayList is always single-dimensional.

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