[java] Checking if a character is a special character in Java

You can use regular expressions.

String input = ...
if (input.matches("[^a-zA-Z0-9 ]"))

If your definition of a 'special character' is simply anything that doesn't apply to your other filters that you already have, then you can simply add an else. Also note that you have to use else if in this case:

if(c == ' ') {
    blankCount++;
} else if (Character.isDigit(c)) {
    digitCount++;
} else if (Character.isLetter(c)) {
    letterCount++;
} else { 
  specialcharCount++;
}