Final Arrays in Java

In Java, the final keyword makes a variable's reference constant, not its contents. When an array is declared as final, you cannot reassign it to point to a new array. However, you can still modify the elements within the array.

What Does Final Mean for Arrays?

If an array is final, it means we can not make it point to a new array, but we can change the elements inside it.

Sample Example: final int[] arr = {10, 20, 30};

Modifying elements inside the array is allowed

arr[2] = 99;

Reassigning the array reference is NOT allowed
arr = new int[]{600, 700, 800}; // Compilation error

Explanation: Here we have declared an array arr as final, which means we can not point arr to a different array, but we can change the value inside the array.

Examples of Final Arrays in Java

Let's now see some examples for better understanding.

Example 1: Modifying Elements of a Final Array

import java.util.*;

class Geeks {
    public static void main(String[] args)
    {

        final int[] arr = {10,20,30};

        arr[2] = 99;

        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
    }
}

10 20 99 

Explanation: The above example shows that we can change the values inside the final array but we can not replace the whole array.

Example 2: Modifying Object State Referenced by a Final Variable

class Geeks {
  
    int p = 20;
    public static void main(String args[])
    {
        final Geeks t = new Geeks();
        t.p = 30;
        System.out.println(t.p);
    }
}

30

Explanation: The above example shows that we can change values inside a final object, but can not replace the object itself.

Example 3: Compilation Error When Reassigning Final Reference

Here is Java program to illustrate final arrays where compilation error is thrown

// Main class
class Geeks {

    int p = 20;

    // Main driver method
    public static void main(String args[])
    {

        // Creating objects of above class
        final Geeks t1 = new Geeks();
        Geeks t2 = new Geeks();

        // Assigning values into other objects
        t1 = t2;

        System.out.println(t1.p);
    }
}

Output:

Note: We cannot assign a value to final variable t1.

Explanation: Above program compiles without any error and program 2 fails in compilation. Let us discuss why the error occurred. So a final array means that the array variable which is actually a reference to an object, cannot be changed to refer to anything else, but the members of the array can be modified. Let us propose an example below justifying the same.

Example 4: Final Array Reference and Reassignment.

Here is Java Program to Illustrate Reassignment Error in Final Array

// Main class
class Geeks {

    // Main driver method
    public static void main(String args[])
    {
        // Declaring a final array
        final int arr1[] = { 1, 2, 3, 4, 5 };

        // Declaring normal integer array
        int arr2[] = { 10, 20, 30, 40, 50 };

        // Assigning values to each other
        arr2 = arr1;
        arr1 = arr2;

        // Now iterating over normal integer array
        for (int i = 0; i < arr2.length; i++)

            // Printing the elements of above array
            System.out.println(arr2[i]);
    }
}

Output:

Explanation: In the above example, we are trying to change a final array that why we are getting an error.

Example 5: Modifying Elements in a Final Array and Attempting Reassignment

Here is demonstrating how to change value inside a final array

// Import Arrays class for toString() method
import java.util.Arrays; 

public class Geeks {
  
    public static void main(String[] args)
    {
        final int[] numbers = { 1, 2, 3, 4, 5 };

        // Assigning new element into the array
        numbers[0] = 10;
        System.out.println(
            "Array after modifying first element: "
            + Arrays.toString(numbers));
    }
}

Output:

Explanation: The above example shows that we can change the values inside a final array but we can not assign a new array to it.

What we can and cannot do with final arrays and objects in Java: