Final Arrays in Java

As we all know final variable declared can only be initialized once whereas the reference variable once declared final can never be reassigned as it will start referring to another object which makes usage of the final impracticable. But note here that with final we are bound not to refer to another object but within the object data can be changed which means we can change the state of the object but not reference. So, as we all know that arrays are also an object so final arrays come into play. The same concept does apply to final arrays that are we can not make the final array refer to some other array but the data within an array that is made final can be changed/manipulated.   

Illustration:

Java

// Java Program to Illustrate Final Arrays
// Can Be Reassigned But Not Re-referred

import java.util.*;

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

        final int[] arr = { 1, 2, 3, 4, 5 };

        arr[4] = 1;

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

Output

1
2
3
4
1

Implementation:

Java

// Java Program to Illustrate Final Arrays

// Importing required classes
import java.util.*;

// Main class
class GFG {

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

        // Declaring a final array
        final int arr[] = { 1, 2, 3, 4, 5 };

        // Iterating over integer array
        for (int i = 0; i < arr.length; i++) {
            arr[i] = arr[i] * 10;
            System.out.println(arr[i]);
        }
    }
}

Output

10
20
30
40
50

Output Explanation: The array arr is declared as final, but the elements of an array are changed without any problem. Arrays are objects and object variables are always references in Java. So, when we declare an object variable as final, it means that the variable cannot be changed to refer to anything else. 

Example A:

Java

// Program 1

// Main class
class Test {

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

Output

30

Example B:

Java

// Java Program to Illustrate Final Arrays
// Where Compiler Error Is Thrown

// Main class
class GFG {

    int p = 20;

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

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

        // Assigning values into other objects
        t1 = t2;

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

Output: Compiler Error: cannot assign a value to final variable t1

Conclusion: 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:

Java

// Java Program to Illustrate Members in Final Array
// Can be Modified

// Main class
class GFG {

    // 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:

Example :

Java

import java.io.*;

public class FinalArrayExample {

    public static void main(String[] args)
    {
        final int[] numbers = { 1, 2, 3, 4, 5 };
        // Attempting to reassign the array reference will
        // result in a compilation error: numbers = new
        // int[] {6, 7, 8, 9, 10};

        // However, individual elements of the array can
        // still be modified:
        numbers[0] = 10;
        System.out.println(
            "Array after modifying first element: "
            + arrays.toString(numbers));
    }
}

Output:

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.