CreditCardValidator.java

package com.andreabaccega.formedittextvalidator;


import android.widget.EditText;

/**
 * This validator takes care of validating the edittext. The input will be valid only if the number is a valid credit card.
 * @author Andrea Baccega <me@andreabaccega.com>
 *
 */
public class CreditCardValidator extends Validator{
  public CreditCardValidator(String _customErrorMessage) {
    super(_customErrorMessage);
  }


  public boolean isValid(EditText et) {
    try {
      return validateCardNumber(et.getText().toString());
    } catch (Exception e) {
      return false;
    }
  }

  /**
   * Validates the credit card number using the Luhn algorithm
   * @param cardNumber the credit card number
   * @return
   */
  public static boolean validateCardNumber(String cardNumber) throws NumberFormatException {
    int sum = 0, digit, addend = 0;
    boolean doubled = false;
    for (int i = cardNumber.length () - 1; i >= 0; i--) {
      digit = Integer.parseInt (cardNumber.substring (i, i + 1));
      if (doubled) {
        addend = digit * 2;
        if (addend > 9) {
          addend -= 9; 
        }
      } else {
        addend = digit;
      }
      sum += addend;
      doubled = !doubled;
    }
    return (sum % 10) == 0;
  }
}