The Casio constructor creates a local array called "abc" which "hides" the class level version. As a result, the class level version never gets any values assigned to it, or indeed any space for elements.
Change this line:
String abc[] = new String[x];
To this:
abc = new String[x];
And try again.
Seriously, you would have found this very, very quickly if you had used the debugger ... it should be your first port of call when you have runtime problems.