Its probably because your class, that is extending Game
is @overriding things that it probably shouldn't be. Or you aren't calling superhttps://github.com/libgdx/libgdx/blob/master/gdx/src/com/badlogic/gdx/Game.java
Examine game, and how setScreen and the current functions behave.
It works a little bit differently then when you use the extend applicationlistener approach.
edit: easy fix
in your "public class SideScroller extends Game"
All those 'blank @override' methods you have, just delete them all
keep the onCreate though, and it should all start working.
easy fix #2
add super.____(); for each @overriden area, specifically the render area
super.render(); inside your @override public void render()
The others should be super'd as well, or just removed completely until you have something to add.
In the superJumper example, he did @override the render, but he also called super.render();
`super` allows the overridden code to still execute, in addition to the code you've added.https://github.com/libgdx/libgdx/blob/master/demos/superjumper/superjumper/src/com/badlogicgames/superjumper/SuperJumper.java