Fill two-dimensional array with Chars from String Input

Question

I'm making a basic game of Tic Tac Toe, accepting player input in the form of a string (i.e. a2). The first char is made into an int called row depending on the letter, the same being said for the second char into col (for array grid[row][col]). I have a block of code that throws a custom exception in the event that the first char isn't a, b, or c, and if the second char isn't 1, 2, or 3:

if(input == null) {
        throw new NullInputException();
    }
    else if(input.length() != 2) {
        throw new InvalidInputException();
    }
    else if(!(input.substring(0,1).equalsIgnoreCase("a") &&
            input.substring(0,1).equalsIgnoreCase("b") &&
            input.substring(0,1).equalsIgnoreCase("c") ||
            input.substring(1).equals("1") &&
            input.substring(1).equals("2") &&
            input.substring(1).equals("3"))) {
        throw new InvalidInputException();
    }

The problem is, this code throws an error even when the input is valid, and I don't know why. I've tried using .charAt() as opposed to .substring(), as well as messed around with my conditional statements. My question is: How do I fix this so that it accepts valid input?

Other questions that just don't help: fill two dimensional array with parts of a string; fill a 2d array with chars of 2 string

You are not using && and || properly. Also, clarify what this has to do with 2 dimensional arrays. — RealSkeptic
– RealSkeptic, Commented Mar 19, 2015 at 15:46
According to your code, the only valid input is a string that contains "abc123". Which means any two character input is immediately invalid because it necessarily is missing at least 4 of the other required characters. — iheanyi
– iheanyi, Commented Mar 19, 2015 at 15:57

Neil Masson · Accepted Answer · 2015-03-19 15:54:51Z

3

Sometimes it is better to write a series of simpler tests which are easier to read and verify

row = input.substring(0,1).toUpperCase();
col = input.substring(1);
boolean validRow = (row.equals("A") ||
                    row.equals("B") ||
                    row.equals("C"));
boolean validCol =
        (col.equals("1") ||
        col.equals("2") ||
        col.equals("3"));

if(!(validRow && validCol)) {

answered Mar 19, 2015 at 15:54

Neil Masson

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Comments

vojta · Accepted Answer · 2015-03-20 11:01:52Z

1

You AND two conditions:

input.substring(0,1).equalsIgnoreCase("a") &&
            input.substring(0,1).equalsIgnoreCase("b")

Both cannot be true in the same time. That is why the result is always false and an exception is thrown.

What you really want is:

String first = input.substring(0,1);
String second = input.substring(1);
    if (!((first.equalsIgnoreCase("a") ||
                first.equalsIgnoreCase("b") ||
                first.equalsIgnoreCase("c")) && 
                (second.equals("1") ||
                second.equals("2") ||
                second.equals("3"))) {
        throw new InvalidInputException();
    }

Small edit for Neil...

edited Mar 20, 2015 at 11:01

answered Mar 19, 2015 at 15:46

vojta

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4 Comments

Alex Over a year ago

But with this, to throw the exception, wouldn't the input have to be bad on both parts (i.e. d4)? If the user simply mis-inputted for one char (i.e. c4) then would this catch the error?

iheanyi Over a year ago

@Alex This only allows a1, a2, a3, b1, b2, b3, c1, c2, c3. If the input is not one of those, then it is invalid.

Alex Over a year ago

My bad. It worked perfectly. I suppose I was just having an issue with my logic. As for the downvoter, care to explain? The solution was perfect.

Neil Masson Over a year ago

It seems that I am the down-voter, but I have absolutely no idea how it happened. I am happy to upvote to rectify this, but the site requires @vojta to edit his answer first since some time has passed since this happened.

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