The JVM doesn't maintain locks unless you ask it to. So yes, it is possible that doSomething could be executed by two threads at once.
You can lock doSomething down to one thread at once by adding a synchronized block within the method, or synchronized keyword to the method signature. However, this will lock the Helper.class object, not any particular instance of Helper. If you have:
doSomething and doSomethingElse could be executed concurrently by two different threads. This is because they lock on two different objects: one locks on the class, the other locks on the instance of the Helper object.
And welcome to the ranch!
Everything is theoretically impossible, until it is done. ~Robert A. Heinlein