JavaCard OS

I need to know the difference between contact and contactless card, especially in APDU command/response field.

If I am going to develop an applet, should I take the contact interface or contactless interface into consideration? I mean whether I need to do some operation for both interface in order to make the applet return the same response for a command?

In fact, there is no difference between the contact and contactless card in APDU field.

However,in the case of contact interface, for APDU command between T=0 and T=1 there is a little difference.
T=0 protocol cannot distinguish between the Lc and Le bytes. So it uses specific status words, such as 61XX and the GET RESPONSE APDU to allow for both command and response data.