first you need to understand what that mean
we can write that in this way
we create Object Zookeeper and we use p reference to point to the Object Zookeeper , now we will invoke the method go() .
yes we can't call no-static method directly from static method but we can use instance Object ( create Object the same way we did in the example "Zookeeper p = new Zookeeper(); " ) to call the no-static method " p.go() "