import org.passay.AllowedCharacterRule;
import org.passay.LengthRule;
import org.passay.PasswordData;
import org.passay.PasswordValidator;
import org.passay.Rule;
import org.passay.RuleResult;

public class PassayExample {
   public static void main(String[] args) {
      //Rule: Password should contains only a, b and c       
      Rule rule1 = new AllowedCharacterRule(new char[] {'a', 'b', 'c'});
      //8 and 16 characters
      Rule rule2 = new LengthRule(8, 16);    

      PasswordValidator validator = new PasswordValidator(rule1, rule2);
      PasswordData password = new PasswordData("abcabcab1");
      RuleResult result = validator.validate(password);

      if(result.isValid()){
         System.out.println("Password validated.");
      } else {
         System.out.println("Invalid Password: " + validator.getMessages(result));            
      }
   }
}

Invalid Password: [Password contains the illegal character '1'.]