Android : Validate half-width Japanese character

I've created method validates if typed character is half-width kana:

public boolean validate(String c) {
    Pattern pattern = Pattern.compile("[\uff61-\uff9f]");
    return pattern.matcher(c).matches();
}

I understood that you want to check is written text composed of only half-width kana, yes? To do this, in onClick() of button which you clicking for validate, write something like this:

for (int i = 0; i < textToValidate.length(); i++) {
    if (validate(textToValidate.charAt(i))) {
        continue;
    } else {
        System.out.println("Text wasn't written in half-width kana.");
        return;
    }
}
System.out.println("Text was written in half-width kana.");

Let me know if my answer is helpful for you. ;)