Correct User Input in Java

Question

Am working on a problem, basic code is shown below, takes 4 possible inputs from the user, and produces a response based on which one is input. However I need to add a test to validate that the only 1 of the 4 possible answers has been input.

I know how I could compare 2 of the 4 inputs however not all 4 at once, can someone give me an idea? Would prefer to figure out the actual code myself but a pointer in the right direction would be beneficial.

So to clarify How to - If input is anything except "Bill, Circular, Postcard or Letter" produce Error Message X

    System.out.println("What type of Letter has been received?");
    System.out.println("Bill, Circular, Postcard or Letter");
    String Letter = kybd.nextLine();

        {
            if (Letter.equalsIgnoreCase("Bill"))  
            {
                System.out.println("Bills must be paid");
            }
            else if (Letter.equalsIgnoreCase("Circular"))
            {
                System.out.println("Circulars are thrown away");
            } 
            else if (Letter.equalsIgnoreCase("Postcard"))
            {
                System.out.println("Postcards are put on the wall");
            } 
            else if (Letter.equalsIgnoreCase("Letter"))
            {
               System.out.println("Personal letters are read and have replies written for them");
            }
        }

Huge hint: if(a && b && c) is valid, as well as if(a || b || c) — Olavi Mustanoja
– Olavi Mustanoja, Commented Oct 23, 2014 at 19:48

Alex · Accepted Answer · 2014-10-23 19:48:37Z

            if (Letter.equalsIgnoreCase("Bill"))  
            {
                System.out.println("Bills must be paid");
            }
            else if (Letter.equalsIgnoreCase("Circular"))
            {
                System.out.println("Circulars are thrown away");
            } 
            else if (Letter.equalsIgnoreCase("Postcard"))
            {
                System.out.println("Postcards are put on the wall");
            } 
            else if (Letter.equalsIgnoreCase("Letter"))
            {
               System.out.println("Personal letters are read and have replies written for them");
            }else{
            System.out.println("ERROR");
            }

I'm such an idiot......*sigh* Looking at this too complicated and the answer is so simple.

ActionCactus · Accepted Answer · 2014-10-23 20:07:01Z

You want to throw an 'else' conditional statement in there, and you may want to look at try and catch blocks, or simply 'throw' a NoSuchElement exception in your 'else' conditional.

Looking at this may be useful to you:

http://docs.oracle.com/javase/tutorial/essential/exceptions/throwing.html

Throwing an exception in an else statement would be a lot like the answer before mine, whereas a try...catch block is pretty much the test you're talking about. So, it could look something like this:

try
{
  Letter != "Bill"  //not exactly how it'd look, but this is a general idea on what you'd do here 
}
catch (NoSuchElementException e)
{
   System.out.println("Not a valid input.");
}

Thanks, will look into those, am sure I'll end up using them soon enough.

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