package com.rgagnon;

public class HelloClass {
 public static void main(String[] args) {
    new HelloClass().say();
 }

 public void say() {
   String className = this.getClass().getName().replace('.', '/');
   String classJar =  
     this.getClass().getResource("/" + className + ".class").toString();
   if (classJar.startsWith("jar:")) {
     System.out.println("*** running from jar!");
   }
   System.out.println(classJar);
 }
}

>jar cvfm Hello.jar manifest.mft com\rgagnon\HelloClass.class
added manifest
adding: com/rgagnon/HelloClass.class (in=1059) (out=601) (deflated 43%)

>java com.rgagnon.HelloClass
file:/C:/DEV/WORK/JAVA/com/rgagnon/HelloClass.class

>java -jar Hello.jar
*** running from jar!
jar:file:/C:/DEV/WORK/JAVA/Hello.jar!/com/rgagnon/HelloClass.class