Enums and Enum Methods

Part of the Object Oriented Programming section of Coddy's Java journey — lesson 50 of 87.

An enum (enumeration) is a special class type that represents a fixed set of constants. Instead of using arbitrary integers or strings to represent options like days of the week or order statuses, enums provide type-safe, readable values.

enum Day {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}

Day today = Day.MONDAY;
System.out.println(today);  // Prints: MONDAY

Enums are more than simple constants—they're full classes. You can add fields, constructors, and methods to them:

enum Size {
    SMALL(10), MEDIUM(20), LARGE(30);
    
    private int price;
    
    Size(int price) {
        this.price = price;
    }
    
    public int getPrice() {
        return price;
    }
}

System.out.println(Size.MEDIUM.getPrice());  // Prints: 20

Every enum comes with useful built-in methods. The values() method returns an array of all constants, while valueOf() converts a string to the matching enum constant. The ordinal() method returns the position of the constant (starting from 0):

for (Day d : Day.values()) {
    System.out.println(d + " is at position " + d.ordinal());
}

Day day = Day.valueOf("FRIDAY");  // Converts string to enum

Enums are ideal when you have a known, fixed set of values that won't change at runtime, making your code safer and more expressive than using plain constants.

Challenge

Easy

Let's build a coffee shop ordering system that showcases the power of enums with fields, constructors, and methods. You'll create a CoffeeSize enum that stores pricing information and a system to process customer orders.

You'll organize your code across three files:

CoffeeSize.java: Create an enum representing coffee sizes with associated prices. Your enum should have three constants: SMALL, MEDIUM, and LARGE with prices of 2.50, 3.50, and 4.50 respectively.
Each size needs a private price field (double), a constructor to set it, and a getPrice() method to retrieve it. Also add a getDescription() method that returns a string in the format: [size name] - $[price] (for example: SMALL - $2.5)
Order.java: Create a class representing a coffee order. An Order has two private fields: customerName (String) and size (CoffeeSize). Include a constructor to initialize both fields and getter methods for each.
Add a getReceipt() method that returns a multi-line string:
```
Order for: [customerName]
Size: [size description from getDescription()]
Total: $[price from the size]
```
Main.java: Bring your coffee shop to life! You'll receive two inputs: a customer name (String) and a size name (String like "SMALL", "MEDIUM", or "LARGE").
First, use CoffeeSize.valueOf() to convert the size string into the corresponding enum constant. Create an Order with the customer name and size, then print the receipt.

After printing the receipt, print an empty line, then display the full menu by iterating through all CoffeeSize values using the values() method. For each size, print its description on a separate line.

You will receive two inputs in order: customer name and size name (one of "SMALL", "MEDIUM", or "LARGE").

Notice how the enum encapsulates both the size identity and its associated price—much cleaner than using separate constants or magic numbers throughout your code!

Cheat sheet

An enum is a special class type representing a fixed set of constants, providing type-safe, readable values:

enum Day {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}

Day today = Day.MONDAY;
System.out.println(today);  // Prints: MONDAY

Enums can have fields, constructors, and methods:

enum Size {
    SMALL(10), MEDIUM(20), LARGE(30);
    
    private int price;
    
    Size(int price) {
        this.price = price;
    }
    
    public int getPrice() {
        return price;
    }
}

System.out.println(Size.MEDIUM.getPrice());  // Prints: 20

Built-in enum methods:

values() - returns an array of all enum constants
valueOf(String) - converts a string to the matching enum constant
ordinal() - returns the position of the constant (starting from 0)

for (Day d : Day.values()) {
    System.out.println(d + " is at position " + d.ordinal());
}

Day day = Day.valueOf("FRIDAY");  // Converts string to enum

Try it yourself

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        // Read inputs
        String customerName = scanner.nextLine();
        String sizeName = scanner.nextLine();
        
        // TODO: Convert sizeName to CoffeeSize enum using valueOf()
        
        // TODO: Create an Order with the customer name and size
        
        // TODO: Print the receipt
        
        // TODO: Print an empty line
        
        // TODO: Display the full menu by iterating through all CoffeeSize values
        // Hint: Use CoffeeSize.values() to get all enum constants
        
    }
}