Array vs ArrayList in Java

1.8

In Java, following are two different ways to create an array.

  1. Array: Simple fixed sized arrays that we create in Java, like below
          int arr[] = new int[10]   
  2. ArrayList : Dynamic sized arrays in Java that implement List interface.
          ArrayList<Type> arrL = new ArrayList<Type>();
    
          Here Type is the type of elements in ArrayList to
          be created
        

Differences between Array and ArrayList

  • An array is basic functionality provided by Java. ArrayList is part of collection framework in Java. Therefore array members are accessed using [], while ArrayList has a set of methods to access elements and modify them.
    // A Java program to demonstrate differences between array
    // and ArrayList
    import java.util.ArrayList;
    import java.util.Arrays;
    
    class Test
    {
        public static void main(String args[])
        {
            /* ........... Normal Array............. */
            int[] arr = new int[3];
            arr[0] = 1;
            arr[1] = 2;
            System.out.println(arr[0]);
    
            /*............ArrayList..............*/
            // Create an arrayList with initial capacity 2
            ArrayList<Integer> arrL = new ArrayList<Integer>(2);
    
            // Add elements to ArrayList
            arrL.add(1);
            arrL.add(2);
    
            // Access elements of ArrayList
            System.out.println(arrL.get(0));
        }
    }
    

    Output:

    1
    1
  • .

  • Array is a fixed size data structure while ArrayList is not. One need not to mention the size of Arraylist while creating its object. Even if we specify some initial capacity, we can add more elements.
    // A Java program to demonstrate differences between array
    // and ArrayList
    import java.util.ArrayList;
    import java.util.Arrays;
    class Test
    {
        public static void main(String args[])
        {
            /* ........... Normal Array............. */
            // Need to specify the size for array 
            int[] arr = new int[3];
            arr[0] = 1;
            arr[1] = 2;
            arr[2] = 3;
            // We cannot add more elements to array arr[]
    
            /*............ArrayList..............*/
            // Need not to specify size 
            ArrayList<Integer> arrL = new ArrayList<Integer>();
            arrL.add(1);
            arrL.add(2);
            arrL.add(3);
            arrL.add(4);
            // We can add more elements to arrL
    
            System.out.println(arrL);
            System.out.println(Arrays.toString(arr));
        }
    }
    

    Output:

    [1, 2, 3, 4]
    [1, 2, 3]
  • .

  • Array can contain both primitive data types as well as objects of a class depending on the definition of the array. However, ArrayList only supports object entries, not the primitive data types.
    Note: When we do arraylist.add(1); : it converts the primitive int data type into an Integer object. Sample Code:

    import java.util.ArrayList;
    class Test
    {
        public static void main(String args[])
        {
           // allowed
            int[] array = new int[3];
    
            // allowed, however, need to be intialized
            Test[] array1 = new Test[3];
    
            // not allowed (Uncommenting below line causes
            // compiler error)
            // ArrayList<char> arrL = new ArrayList<char>();
    
            // Allowed
            ArrayList<Integer> arrL1 = new ArrayList<>();
            ArrayList<String> arrL2 = new ArrayList<>();
            ArrayList<object> arrL3 = new ArrayList<>();
        }
    }
    
  • .

  • Since ArrayList can’t be created for primitive data types, members of ArrayList are always references to objects at different memory locations (See this for details). Therefore in ArrayList, the actual objects are never stored at contiguous locations. References of the actual objects are stored at contiguous locations.
    In array, it depends whether the arrays is of primitive type or object type. In case of primitive types, actual values are contiguous locations, but in case of objects, allocation is similar to ArrayList.

As a side note, ArrayList in Java can be seen as similar to vector in C++.

 

This article is contributed by Pranjal Mathur. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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