Because LC in cases 3E and 4E can take a large value, the parameter is sent to the card as a three-byte quantity, in the format of 00 LCh LCl starting at ISO7816.OFFSET_LC.
To get the value of LC and the data offset inside the APDU buffer use these two APIs in javacard.framework.APDU:
public short getIncomingLength()
This API call returns the value of LC as expressed in the APDU, whether it is extended or not.
public short getOffsetCdata()
This API call returns the offset where the first byte of the APDU data segment is found.