How to solve the error in the switch / case? Java

Change in:

helados = teclado.next();

By:

helados = teclado.nextLine();

When you use next you only use the first word before the space.

Some tips to determine where the code is failing (without entering debugging tools):

1. Simplify the problem.

Surely you have some indication of where the program is failing: extract the part that you think is failing and see adding complexity until something fails. For example: you have a reading of a string by keyboard, which is passed to a switch , you can put that part in a test class and obviate the keyboard input by testing with the strings that can be expected:

package pruebas;

public class Zzz {

    public static void main(String[] args) {
        test("vaso chico");
        test("vaso mediano");
        test("cucurucho");
        test("xxx");
    }

    public static void test(String option) {
        switch (option) {

            case "vaso chico":
                System.out.println("Seleccionado vaso chico");
                break;

            case "vaso mediano":
                System.out.println("Seleccionado vaso mediano");
                break;

            case "cucurucho":
                System.out.println("cucurucho");
                break;

            default:
                System.out.println("Error !" + option);
                System.out.println("---> " + option); // HACK: trace
        } // switch
    }

} // class

2. Use traces.

In the previous code I added the line:

System.out.println("---> " + option); // HACK: trace

In case you enter the default condition you will know which string is being evaluated. If the string is not what you expected, check its origin.

3. Combine paths with completions.

You can add traces to determine if the program passes through certain points and end execution at different points.

// code
// ...
System.out.println(" line 12" ); // HACK: trace
// code
// ...
System.out.println(" line 17" ); // HACK: trace
// code
// ...
System.out.println(" line 23" ); // HACK: trace
System.exit(0);

4. Refactor to make the code easier to read and interpret.

Use methods to separate the different actions. Also, if you have repeated parts you can restructure to reduce the code easily, for example, notice that you are repeating the following in each case of the switch :

System.out.println(i + ".Ingrese Cantidad : ");
cantidad = teclado.nextInt();

Ok, do not you want to ask if they do not introduce a valid option? That's why you can not enter this part before the switch, but if you can use a method to ask the amount:

cantidad = getQuantity(teclado, i);

//...

private static int getQuantity(Scanner scn, int n) {
    System.out.println(n + ".Ingrese Cantidad : ");

    return scn.nextInt();
}

5. Use meaningful names for the variables.

This does not matter as much as you write your code today, but in 2 weeks you'll see ... I still do not know what the i does in the for , for that the method that I just put you is so clarifying.

6. Use try-catch blocks with generic exceptions.

When exceptions are thrown you have automatic tracings that help you determine what's wrong. Putting the "chunk" of code where the program fails within this structure usually helps.

For the method that returns the amount, which by the way I think will fail if you do not enter a number:

private static int getQuantity(Scanner scn, int n) {
    try {
        System.out.println(n + ".Ingrese Cantidad : ");
        return scn.nextInt();

    } catch(Exception e) {}

    return 0; // default
}