final variables

Learn constant-value variables with final.

What is final?

The final keyword marks a variable as not reassignable. Once you give it a value, it cannot change. Such variables are called constants.

final double PI = 3.14;
PI = 3.15; // compile error

Constants are usually named in ALL_CAPS: MAX_SPEED, PI, URL. This signals to other developers that the value does not change.

Constants are ideal for values that stay the same across the program: math constants, configuration values, limits.

Write a Main class with a main method. Assign 120 to final int MAX_SPEED. Print it with println.

Show example solution

public class Main {
    public static void main(String[] args) {
        final int MAX_SPEED = 120;
        System.out.println(MAX_SPEED);
    }
}

When a value will not change throughout the program, using final is good practice. It prevents accidental changes and states the intent clearly.

Common examples:

Local variables can also be final; variables used in lambda expressions must be effectively final.

Complete the final constant

final double PI = ____;

Show answer

final double PI = 3.14;