If you have never played Minecraft, then this is how the mechanics of the launcher work.
The user can download a JAR (Or a JAR packaged into an EXE), which has absolutely no code for the Minecraft client at all. This is deemed the launcher. When the launcher is started, it displays a login screen with news etc. Then, after logging in, the launcher then runs the main Minecraft core, minecraft.jar. If it is not present on the system, it downloads it. The Minecraft launcher doesn't need any external Java libraries to run either.
How does it do this?
I'm currently trying to replicate the functionality, however, when I export as a runnable JAR in Eclipse, when I try launch it, it prints "Could not find main class launcher.jar. Program will exit" (this is on the console, I want to be able to double click the JAR and have it launch)
File file = new File(System.getProperty("user.dir") + "/lessur.jar");
System.setProperty("org.lwjgl.librarypath", System.getProperty("user.dir") + "natives");
URLClassLoader classLoader;
classLoader = URLClassLoader.newInstance(new URL[]{file.toURI().toURL()});
classLoader.loadClass("zombie.engine.Lighting2").newInstance();