Appium provides keycodes for the alphabets only in the lowercase. If we have to send any alphabet in uppercase then we have to send the keycode of that alphabet with the shift keycode. Practically also we first press the shift key and then press the desired key.
Appium library provides a method through which a key event is send along with an Android metastate to an Android device.
pressKeyCode(integer key, Integer metastate)
Lets take a scenario of sending the alphabet "K" in uppercase.
39 is the keycode for K and 59 is the keycode for Shiftkey.