What is the purpose of declaring a variable as final?

• A. A final variable's value can be changed.
• B. Final variables must be initialized later.
• C. A final variable's value cannot be changed.
• D. Final variables only exist within methods.

Answer: (C)

Declaring a variable as final establishes that the variable's value is immutable after its initial assignment. This means once the final variable is assigned a value, it cannot be modified or reassigned throughout its lifecycle in the program. This characteristic is particularly useful when defining constants or ensuring that specific values remain unchanged, which can help in maintaining consistency and stability within the program.

For example, when you declare a constant such as final int MAX_SPEED = 90;, you are indicating that MAX_SPEED should always have the value of 90, and any attempt to assign a different value to MAX_SPEED later in the code will lead to a compilation error. This enforces a level of safety and reliability in the code, as it prevents inadvertent changes that could lead to bugs or unpredictable behavior during execution.

The other answer choices relate to misunderstandings about the nature of final variables. While a final variable must be initialized at the time of declaration or in the constructor (which makes the statement about later initialization incorrect), a final variable does not imply it exists only within methods, as it can also be declared at the class level.