Communicating Objects

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.