The type effects which methods will throw a LtInvalidStateException.
e.g. You cannot call getYear() if the type is not date, dateTime, gYear or gYearMonth as no Year element is available.
    
public final class DateTimeType implements java.io.Serializable
{
    public static DateTimeType yearZero = new DateTimeType(YEAR_ZERO);
    public static DateTimeType dateTime = new DateTimeType(DATE_TIME);
    public static DateTimeType date = new DateTimeType(DATE);
    public static DateTimeType gYearMonth = new DateTimeType(G_YEAR_MONTH);
    public static DateTimeType gYear = new DateTimeType(G_YEAR);
    public static DateTimeType time = new DateTimeType(TIME);
    public static DateTimeType gDay = new DateTimeType(G_DAY);
    public static DateTimeType gMonth = new DateTimeType(G_MONTH);
    public static DateTimeType gMonthDay = new DateTimeType(G_MONTH_DAY);

    public String toString();
}