Using  Scala we can easily create lock free multi-threaded code, while still maintaining a familiar programming model.

There are two issues of writing multi-threaded code: synchronizing shared access to resources and running code asynchronously. In Java this is usually done with locks and implementing interfaces that wrap the asynchronous code. This leads to code that is cumbersome to write, error prone and inefficient in how it uses threads (since a thread may block for an unspecified time waiting on a lock).

In Scala we have actors (of course there are actor libraries for Java also, they are just less popular).  However, using actors means giving away on type safety (we cannot know the exact set of messages an actor handled) and is also cumbersome to use as a replacement for method calls.