includes/org/apache/poi/ss/usermodel/DateUtil.java
public static boolean isInternalDateFormat(int format) {
            switch(format) {
                // Internal Date Formats as described on page 427 in
                // Microsoft Excel Dev's Kit...
                case 0x0e:
                case 0x0f:
                case 0x10:
                case 0x11:
                case 0x12:
                case 0x13:
                case 0x14:
                case 0x15:
                case 0x16:
                case 0x2d:
                case 0x2e:
                case 0x2f:
                    return true;
            }
       return false;
    }
/**
     * Given a format ID this will check whether the format represents
     *  an internal excel date format or not.
     * @see #isADateFormat(int, java.lang.String)
     */
Given a format ID this will check whether the format represents
an internal excel date format or not.
Given a format ID this will check whether the format represents an internal excel date format or not .
public static boolean isInternalDateFormat(int format) {
            switch(format) {
                case 0x0e:
                case 0x0f:
                case 0x10:
                case 0x11:
                case 0x12:
                case 0x13:
                case 0x14:
                case 0x15:
                case 0x16:
                case 0x2d:
                case 0x2e:
                case 0x2f:
                    return true;
            }
       return false;
    }
public static boolean isInternalDateFormat ( int format ) { switch ( format ) { case 0x0e : case 0x0f : case 0x10 : case 0x11 : case 0x12 : case 0x13 : case 0x14 : case 0x15 : case 0x16 : case 0x2d : case 0x2e : case 0x2f : return true ; } return false ; }
Given a format ID this will check whether the format represents
  an internal excel date format or not.
Given a format ID this will check whether the format represents an internal excel date format or not .
// Internal Date Formats as described on page 427 in
 // Microsoft Excel Dev's Kit...
