Java comes with a built-in multi-threading model based on shared data and locks. To use this model, you decide what data will be shared by multiple threads and mark as “synchronized” sections of the code that access the shared data.
It also provides a locking mechanism to ensure that only one thread can access the shared data at a time. Lock operations remove possibilities for race conditions but simultaneously add possibilities for deadlocks. In Scala, you can still use Java threads, but the “Actor model” is the preferred approach for concurrency.