Final Arrays in Java

In Java, final is a keyword. It is a non-access modifier. It means that it restricts modifications of the variable, methods, and classes. It ensures that once an entity is declared as final, it can be assigned and defined once.

On the other hand, a reference variable, once declared final, can never be reassigned because it refers to another object that makes usage of the final useless.

Here, a point to note is that we are bound not to refer to another object. But in context to the object, data can be changed. It means that we can change the state of the object, not the reference.

In Java, an array is treated as an object, and object variables are always reference in Java. Here, the concept of a final array comes into play.

In this section, we will discuss the final array in Java with an example and Java program for the same.

Final Array

In Java, when we declare an array as final, it means that the reference to the array cannot be changed after initialization. In simple words, final applies to the reference, not to the contents of the array.

Let’s understand it with an example.

Final Array Example

Consider the following code snippet.

Key Points

Immutable Reference: Once a final array is assigned, we cannot point the array variable to another array or null.

Mutable Contents: We can update, add, or remove elements in the array (depending on the type of array).

This behavior is often used to ensure the integrity of a reference while allowing modifications to the data it holds.

Implementation of Final Array

Output:

 7 2 3 10 5 6 

In the above example, we observe that the array is declared as final, but the elements of the array are changed. When we remove the comment at line 10, it gives a compilation error.

Output:

 8, 11, 14, 17, 19, 21 

Let’s discuss some other Java programs related to final array.

Program 1: Modifying Elements in a Final Array

Output:

 [Apple, Pineapple, Blueberry, Banana, Cherry] 

Explanation

The program demonstrates that declaring an array as final in Java makes its reference immutable, meaning the array cannot be reassigned, but individual elements can still be modified. The program initializes a final String array, modifies some elements, and prints the updated values of the array.

Program 2: Passing Final Array to a Method

We can pass a final array to a method. It also modifies the element of the array.

Output:

 [10, 20, 100, 200, 300, 60, 70] 

Explanation

The program demonstrates the final array when passed as a method parameter in Java, where the reference itself cannot be reassigned, but individual elements can be modified. The modifyArray() method updates the third, fourth, and fifth elements (according to index value) of the array, and this change persists outside the method.

Program 3: Multi-Dimensional Final Array

Similarly, we can declare a multi-dimensional array as final.

Output:

 [[56, 2, 3], [4, 5, 19], [7, 45, 29]] 

Explanation

The program demonstrates a final 2D array in Java, where individual elements can be modified, but reassigning the reference to a new array is not allowed. The program initializes a final 2D array matrix, modifies some of its elements, and then prints the updated matrix. Attempting to assign a new array to the matrix would result in a compilation error.

Program 4: Final Array of Objects

When using an array of objects, we can modify the object's properties but not the reference.

Output:

 10, 2 3, 40 

Explanation

The program demonstrates a final array of objects. It ensures that the reference cannot be reassigned but allows modification of its elements.

Program 6: Final Array Inside a Constructor

Output:

 10 99 30 

Explanation

The program demonstrates a final array in a constructor that ensures that the reference cannot be reassigned but allows modification of its elements. The DataHolder class has a final array data, initialized through the constructor.

The modifyData() method changes the value at a given index, showing that elements can be updated. In main(), an object is created with an integer array, the second element is modified, and the updated array is displayed.