I have this test app:
import java.applet.*;
import java.awt.*;
import java.net.URL;
public class Test extends Applet
{
public void init()
{
You don't need the slash at the start when getting a resource from a ClassLoader, because there's no idea of a "relative" part to start with. You only need it when you're getting a resource from a Class where relative paths go from the class's package level.
In addition, you don't want Test.class.getClass() as that gets the class of Test.class, which will be Class.
In other words, try either of these lines:
URL viaClass=Test.class.getResource("/assets/pacman.png");
URL viaLoader=Test.class.getClassLoader().getResource("assets/pacman.png");