Need some help understanding ClassLoader

When I use a statement like:

classLoader.loadClass()

What String am I putting inside the parentheses? Is it: 1. The full absolute path to the class file? 2. A relative path to the class file (dependent on where the ClassLoader is made)? 3. Just the file name of the class? 4. Just the class name? This is what I have been trying to work with so far:

public void scanFileSystem() throws ClassNotFoundException
    {
        if(packageName.startsWith("/"))
        {
            packageName = packageName.substring(1);
        }
        packageName = packageName.replaceAll("%20", " ");
        File file = new File(packageName);
        if(file.isDirectory())
        {
            for(File classFile : Objects.requireNonNull(file.listFiles()))
            {
                if(classFile.getName().endsWith(".class"))
                {
                    Class c = loadClass(classFile);
                    if(c != null)
                    {
                        hiddenClasses.add(c);
                    }
                }
            }
        }
        else
        {
            System.out.println(packageName);
            System.out.println("not a directory");
            System.exit(0);
        }
    }

    public Class loadClass(File file)
    {
        ClassLoader classLoader = Solution.class.getClassLoader();
        if(file.getName().endsWith(".class"))
        {
            try
            {
                Class c = classLoader.loadClass(packageName + "/" + file.getName());
                return c;
            }
            catch(ClassNotFoundException e)
            {
                e.printStackTrace();
            }
        }
        return null;
    }
}

Needless to say, this doesn't work at all.