Pretty sure it isn't possible to extend your classes with the main class. Also don't use a while loop in your bank() method. If statement does the job. In your walk method you have double brackets in IF condition for no reason. What you should do is making a constructor in your bank class and pass the Methodprovider through it. No idea if I am explaining it right, here an example:
Public class Banking {
Methodprovider s;
public Banking (MethodProvider s) {
this.s = s;
}
public void bank() {
// Here your banking method.
}
}
public class Woodcutter extends Script {
public int onLoop() {
Banking banking = new Banking(this);
banking.bank();
return 100;
}
}