How does Intellij idea debug's device run under the cover?

I am just very interested how the debug runs under the cover. Let's say we have a jar project, including two modules A and B.

A is just service module. And B is the main module, which has the entrance main method. B refers A.

A's compiled class is under A's target folder, and B's compiled class is under B's target folder. As I understand, when the debug runs, it runs from B's targer folder, from B's complied main method.

But when debug running, how does it find A's compiled class while they are not in the same folder? Does it automatically put A's class in classpath?

Many thanks!