Of course. To get the work done, humans (and objects) need to ask each other to do their specialized tasks and need to give each other information necessary for the jobs.
A running program is a collection of objects that are each doing their own task and communicating with other objects. The picture shows a running program (or a pizza shop). The jagged lines represent communication. The boss is special and so is drawn with dotted lines.
In Java programs the main() method is
special because it is where the Java interpreter
starts the whole program running.
The main() method is a static
method,
which means that there will be only one instance of
it and that it exists (as part of a class)
before any objects have been created.
Say that after a few days your object-oriented pizza business gets more orders than it can handle. What will you do?