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Switch Statement

Switch statements are used to perform different actions based on different conditions.

Here we have a long example, where the user types a command, and the program runs the code for a given command. (This is sometimes referred to as a shell or command loop).

Notice how we first get a command from the user, look at each possibility, and do something specific if we find a matching command string. Otherwise, we print an error message.

String lastCommand = getCommandFromUser();

switch(lastCommand){
    case "exit":
        System.out.println("so long!");
        break;
    case "run":
        System.out.println("running simulation...");
        runSim();
        break;
    case "rename":
        renameSim();
        break;
    case "delete":
        if (makeSureDeleteIsOkay()) {
            deleteSim();
        } else {
           System.out.println("delete cancelled...");
        }
        break;
    case "new":
        createNewSim();
        break;
    case "help":
        showHelpToUser();
        break;
    default:
        System.out.println("command not found: try again or type help");
}

Switch statements can be quite elaborate (and in this case much better than a whole lot of IF statements).

Here’s the exercise from the if section. Oftentimes, you can write a switch statement in if statements, or a bunch of if statements as a switch statement. This time, you should use a switch statement.

Exercise: Age Verification with Switch Statement

Write code to check if a user is old enough to drink. (Using a switch)

  • if the user is under 18. Print out "cannot party with us"

  • Else if the user is 18 or over. Print out "party over here"

  • Else print out "I do not recognize your age"

Finally, make sure to change the value of the age variable to output different results.
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