Constants (static final)

Part of the Object Oriented Programming section of Coddy's Java journey — lesson 18 of 87.

Combining static and final creates a constant - a value that belongs to the class and can never change. This is the standard way to define constants in Java.

public class GameSettings {
    public static final int MAX_PLAYERS = 4;
    public static final double GRAVITY = 9.81;
    public static final String GAME_TITLE = "Space Adventure";
}

By convention, constant names use UPPER_SNAKE_CASE to distinguish them from regular variables. Since they're both static and final, you access them through the class name and their values are guaranteed to never change:

System.out.println(GameSettings.MAX_PLAYERS);  // 4
// GameSettings.MAX_PLAYERS = 8;  // Error! Cannot modify

Constants are typically declared public because they're meant to be shared across your application. Think of values like Math.PI - it's a public static final constant that any code can use.

Why use constants instead of hardcoded values? If you write 4 throughout your code and later need to change it to 6, you'd have to find and update every occurrence. With a constant like MAX_PLAYERS, you change it in one place.

Constants also make code more readable - MAX_PLAYERS is clearer than a mysterious 4.

Challenge

Easy

Let's build a MathConstants utility that stores important mathematical values as constants, along with a CircleCalculator that uses those constants to perform calculations.

You'll create two files to organize your code:

MathConstants.java: Create a class that holds mathematical constants using public static final fields:
- PI with value 3.14159
- E (Euler's number) with value 2.71828
- GOLDEN_RATIO with value 1.61803
Remember to use UPPER_SNAKE_CASE for constant names!
Main.java: Use your constants to perform circle calculations. You'll receive a radius as input and print three lines:
- The area of the circle: Area: [value]
- The circumference of the circle: Circumference: [value]
- The diameter scaled by the golden ratio: Golden Diameter: [value]

For the calculations:

Area = PI * radius * radius
Circumference = 2 * PI * radius
Golden Diameter = 2 * radius * GOLDEN_RATIO

You will receive one input: the radius (double).

Format all output values to 2 decimal places using String.format("%.2f", value). Access your constants through the class name, like MathConstants.PI.

Try it yourself

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double radius = scanner.nextDouble();
        
        // TODO: Calculate the area using MathConstants.PI
        // Formula: PI * radius * radius
        
        // TODO: Calculate the circumference using MathConstants.PI
        // Formula: 2 * PI * radius
        
        // TODO: Calculate the golden diameter using MathConstants.GOLDEN_RATIO
        // Formula: 2 * radius * GOLDEN_RATIO
        
        // TODO: Print the results formatted to 2 decimal places
        // Use String.format("%.2f", value) for formatting
        // Output format:
        // Area: [value]
        // Circumference: [value]
        // Golden Diameter: [value]
        
    }
}