getClassLoader().getResource() returns null

• When you use .getClass().getResource(fileName) it considers the location of the fileName is the same location of the of the calling class.
• When you use .getClass().getClassLoader().getResource(fileName) it considers the location of the fileName is the root - in other words bin folder

It hits NullPointerException if the file is actually not exist there.

Source:

package Sound;
public class ResourceTest {
    public static void main(String[] args) {
        String fileName = "Kalimba.mp3";
        System.out.println(fileName);
        System.out.println(new ResourceTest().getClass().getResource(fileName));
        System.out.println(new ResourceTest().getClass().getClassLoader().getResource(fileName));

Output:

Kalimba.mp3
file:/C:/Users/User/Workspaces/MyEclipse%208.5/JMplayer/bin/Sound/Kalimba.mp3
file:/C:/Users/User/Workspaces/MyEclipse%208.5/JMplayer/bin/Kalimba.mp3
    }
}

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<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");

I would do it this way:

final InputStream stream;

stream = Test.class.getResourceAsStream("assets/pacman.png");
System.out.println("Stream = " + stream);

"/assets/pacman.png" is an absolute location whle "assets/pacman.png" is a relative location.