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.

Cheat sheet

Combining static and final creates a constant - a value that belongs to the class and can never change:

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. Access constants through the class name:

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

Constants are typically declared public to be shared across your application. They make code more maintainable and readable by replacing hardcoded values with meaningful names.

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]
        
    }
}