Vessel, ship IMO number validator, validation function

gistfile1.java

public static final boolean isImoValid(String imo) {
	if (imo == null || imo.length() != 7) {
		return false;
	}
	char[] a = imo.toCharArray();
	int sum = 0;
	for(int i = 0; i < 6; i++) {
		sum += (a[i]-48)*(a.length-i);
	}
	return sum % 10 == a[6]-48;
}