Is it acceptable to use a switch statement within a switch statement?

Question

I know my documentation is not superb.

This program is to create a Rock, Paper, Scissors Game:

I initially struggled with getting the case statements withing case statements to work properly but I feel like I resolved the issue.

My question: is this an acceptable implementation of nesting a switch statement within a switch statement. Otherwise, I could put an if statement within the userChoice Switch statement instead.

public static void main(String[] args) {

    // Variable declarations
    Scanner keyboard = new Scanner(System.in);
    Random rand = new Random();
    int sentinel = 4;
    int userChoice;
    int computerChoice;

    // Display Rock, Paper, Scissors menu
    menu();

    // Obtain user's choice
    userChoice = validOption("\nPlease make a selection: ", 1, 4);

    // Display game results
    while (userChoice != sentinel) {
        switch (userChoice) {
            case 1:
                // Generate computer's choice
                computerChoice = rand.nextInt(3) + 1; 
                System.out.println("Computer's choice: " + computerChoice);

                // Determine outcome of the round
                switch (computerChoice) {
                    case 1:
                        System.out.println("Rock cannot defeat Rock. Draw.");
                        break;
                    case 2:
                        System.out.println("Paper covers Rock. Computer wins.");
                        break;
                    case 3:
                        System.out.println("Rock smashes Scissors. You win!");
                        break;
                }
                // Display menu selection and obtain user choice
                menu();
                userChoice = validOption("\nPlease make a selection: ", 1, 4);
                break;

            case 2: 
                // Generate computer's choice
                computerChoice = rand.nextInt(3) + 1; 
                System.out.println("Computer's choice: " + computerChoice);

                // Determine outcome of the round
                switch (computerChoice) {
                    case 1:
                        System.out.println("Paper covers Rock. You win!");
                        break;
                    case 2:
                        System.out.println("Paper cannot defeat Paper. Draw.");
                        break;     
                    case 3:
                        System.out.println("Scissors cut Paper. Computer wins.");
                        break;
                }
                //Display menu selection and obtain user choice
                menu();
                userChoice = validOption("\nPlease make a selection: ", 1, 4);
                break;

            case 3:
                // Generate computer's choice
                computerChoice = rand.nextInt(3) + 1; 
                System.out.println("Computer's choice: " + computerChoice);
                // Determine outcome of the round
                switch (computerChoice) {
                    case 1:
                        System.out.println("Rock smashes Scissors. Computer wins.");
                        break;
                    case 2:
                        System.out.println("Scissors cut Paper. You win!");
                        break;
                    case 3:
                        System.out.println("Scissors cannot defeat Scissors. Draw.");
                        break;
                }
                // Display menu selection and obtain user choice
                menu();
                userChoice = validOption("\nPlease make a selection: ", 1, 4);
                break;
        }
    }     
    System.out.println("Game Over.");
}

// Create menu method
public static void menu () {
    System.out.println("\n1 = Rock");
    System.out.println("2 = Paper");
    System.out.println("3 = Scissors");
    System.out.println("4 = End Game\n");
}

/**
 * Protects option input from incorrect value (non-numeric, too high or too low)
 * @param prompt
 * @param minValue
 * @param maxValue
 * @return 
 */
public static int validOption (String prompt,
                                int minValue,
                                int maxValue) {
    Scanner keyboard = new Scanner (System.in);
    int value;
    String errorMessage = "Incorrect value. Please select options "
            + "1, 2, 3 or 4\n";
    do {
        System.out.print(prompt);
        if (keyboard.hasNextInt()) {
            value = keyboard.nextInt();
            if (value < minValue || value > maxValue) {
                System.out.println(errorMessage);
            } else {
                break; // Exit loop.
            }
        } else {
            System.out.println(errorMessage);
        }
        keyboard.nextLine(); // Clears buffer.
    } while (true);
    return value;
}

}

Of course it will work, but this makes code hard to read and understand. I cannot say it is a good practice to do like that. Instead try extract some stuff to separate methods at least. — ikos23, Apr 07 '18 at 18:37

score 2 · Answer 1 · answered Apr 07 '18 at 18:41

IMHO, as long as it is readable, writing switch statements inside switch statements is fine per se. To make the code more readable, you can use constants instead of 1, 2, 3 to refer to the choices:

final int ROCK = 1;
final int PAPER = 1;
final it SCISSORS  = 1;

Your switches can look like this:

switch (computerChoice) {
    case ROCK:
        System.out.println("Rock cannot defeat Rock. Draw.");
        break;
    case PAPER:
        System.out.println("Paper covers Rock. Computer wins.");
        break;
    case SCISSORS:
        System.out.println("Rock smashes Scissors. You win!");
        break;
}

Another thing you could improve is to move these two parts out of the outer switch:

// Generate computer's choice
computerChoice = rand.nextInt(3) + 1; 
System.out.println("Computer's choice: " + computerChoice);

// and

menu();
userChoice = validOption("\nPlease make a selection: ", 1, 4);

since you are doing this in every case.

You can also extract the inner switch statements into methods like this:

private static handlePlayerRock() {
    // add the inner switch for the case ROCK of the outer switch here
}

private static handlePlayerScissors() {
    // add the inner switch for the case SCISSORS of the outer switch here
}

private static handlePlayerPaper() {
    // add the inner switch for the case PAPER of the outer switch here
}

Your switch will then look like this:

switch (userChoice) {
    case ROCK: handlePlayerRock();
    case PAPER: handlePlayerPaper();
    case SCISSORS: handlePlayerScissors();
}

There are more advanced ways to use for this problem other than nested switches. You can put all the possibilities into a HashMap<Combination, String>, where Combination is a class that represents the player and the computer's choices. The map will contain things like:

(ROCK, ROCK) -> "Rock cannot defeat Rock. Draw."
(ROCK, PAPER) -> "Paper covers Rock. Computer wins."
...

And you can just use both the computer's and the player's choice to access the value associated with the key.

Is it acceptable to use a switch statement within a switch statement?

1 Answers1