Credit Card Detection

detect.java

public static CardType fromCardNumber( String cardNumber ) {
    if ( cardNumber == null )
        return CardType.Null;
    if ( cardNumber.matches( "^4[0-9]*$" ) )
        return CardType.Visa;
    if ( cardNumber.matches( "^5[1-5][0-9]*$" ) )
        return CardType.MasterCard;
    if ( cardNumber.matches( "^3[47][0-9]*$" ))
        return CardType.Amex;
    if ( cardNumber.matches( "^6(?:011|5)[0-9]*$" ))
        return CardType.Discover;
    return CardType.Null;
}

exact.java

public static CardType Null = new CardType( "^[0-9]+$", "" );
public static CardType Visa = new CardType( "^4[0-9]{6,}$", "visa" );
public static CardType MasterCard = new CardType( "^5[1-5][0-9]{5,}$", "master card" );
public static CardType Amex = new CardType( "^3[47][0-9]{5,}$", "amex" );
public static CardType Discover = new CardType( "^6(?:011|5[0-9]{2})[0-9]{3,}$", "discover" );