Java Program to show usage of Enum which prints the size of coffee mug

Program

class Coffee
{
	enum CoffeeSize { SMALL, MEDIUM, LARGE }
	CoffeeSize size;
}
public class CoffeeEnum
{
	public static void main(String[] args)
	{
		Coffee coffee = new Coffee();
		coffee.size = Coffee.CoffeeSize.MEDIUM;
		System.out.println("Size of coffee mug is: " + coffee.size);
		coffee.size = Coffee.CoffeeSize.SMALL;
		System.out.println("Size of coffee mug is: " + coffee.size);
		coffee.size = Coffee.CoffeeSize.LARGE;
		System.out.println("Size of coffee mug is: " + coffee.size);
	}
}

Purpose

• To show how to use Java enum to define a set of constants (in this case, different coffee sizes).
• To illustrate how to use enum in practice by associating it with an instance of a class and displaying its values.

1. Define an enum

enum CoffeeSize { SMALL, MEDIUM, LARGE }

• enum CoffeeSize: Defines three constants for coffee sizes — SMALL, MEDIUM, and LARGE.
• Each constant represents a specific size.
• enum helps in defining a fixed set of related constants, which makes the code more readable and maintainable.

2. Coffee Class

class Coffee
{
	enum CoffeeSize { SMALL, MEDIUM, LARGE }
	CoffeeSize size;
}

• The Coffee class has an instance variable size of type CoffeeSize.
• This size variable represents the size of a coffee mug and will hold one of the values (SMALL, MEDIUM, or LARGE) from the CoffeeSize enum.

3. Main Method

public static void main(String[] args)
{
	Coffee coffee = new Coffee();
	coffee.size = Coffee.CoffeeSize.MEDIUM;
	System.out.println("Size of coffee mug is: " + coffee.size);
	coffee.size = Coffee.CoffeeSize.SMALL;
	System.out.println("Size of coffee mug is: " + coffee.size);
	coffee.size = Coffee.CoffeeSize.LARGE;
	System.out.println("Size of coffee mug is: " + coffee.size);
}

• Creating an Instance: A Coffee object is instantiated.
• Assigning Sizes:
  • The coffee.size is assigned Coffee.CoffeeSize.MEDIUM.
  • The coffee.size is then changed to Coffee.CoffeeSize.SMALL.
  • Finally, it is set to Coffee.CoffeeSize.LARGE.
• Printing Sizes: The size of the coffee mug is printed each time it is set to a different enum constant.

Key Concepts

1. enum in Java:

   • enum is a special class in Java used to define a collection of constants.
   • It helps in defining a clear and fixed set of related values (like SMALL, MEDIUM, and LARGE coffee sizes).
   • enum makes the code easier to read and maintain since it restricts the number of possible values.

2. Encapsulation of Constants:

   • enum constants can be used to enforce a controlled set of possible values, which is useful for scenarios where the set of values should be restricted and predictable.

3. Instance Variables:

   • The size variable in the Coffee class is an instance of the CoffeeSize enum, representing the coffee's size.

4. Usage in Main Method:

   • Demonstrates changing and printing different sizes of coffee mugs, showing the flexibility of enums.

Output

Size of coffee mug is: MEDIUM
Size of coffee mug is: SMALL
Size of coffee mug is: LARGE