What effect does the reserved word 'final' have on a variable?

The reserved word 'final' in programming serves to create a constant in that context, which means that once a variable is assigned a value using 'final', it cannot be modified or reassigned later in the program. This guarantees that the value remains unchanged throughout the variable's lifecycle, enforcing immutability.

Using 'final' can be particularly useful for defining constants that are integral to the program's logic, as it prevents accidental changes that could lead to errors or unintended behavior. By ensuring that the variable's value is fixed, developers can write clearer and more reliable code, reducing bugs that arise from unintentional variable modifications.

In contrast, the other options do not accurately represent the functionality of 'final.' The concept does not extend the scope of a variable or affect its data storage capacity. Its primary purpose is to safeguard the variable's assigned value by prohibiting changes after it has been set.