Before developing a plug-in for ImageJ / Fijian must think that kind is going to be, and this depends on the input data:
Its interfaces are:
void run (java.lang.String arg) //this method runs the plugin. "arg" is an argument to the plugin, which can be empty string.
void run (ImageProcessor ip) //this method runs the plugin. It takes the image processor and it works on as an argument.
int setup (java.lang.String arg, ImagePlus imp) //this method sets up the plugin filter use. The "arg" string has the same function as in the run method of the PlugIn interface.
//this is a subclass of an AWT frame that implementes the PlugIn
void run (java.lang.String arg) //declared in the PlugIn interface is implemented and can be overwritten by your plugin's run method.