I'm working on a 2d java game on Slick engine and I always wondered how to make swing effects when striking with a sword? How to code something like this what's in the game Hollow Fear? Example from YouTube here.
You've got two simple options:
Generate particles based on the velocity of the sword in the form of motion lines
Draw up sprites and iterate through these using frames (couple of examples at http://www.spriters-resource.com/genesis_32x_scd/shinobi3/sheet/20808/)