Building Blocks - Java Concurrency in Practice - page 127

Listing 5.20. Factorizing Servlet that Caches Results Using Memoizer .
Summary of Part I
We've covered a lot of material so far! The following “concurrency cheat sheet” summarizes
the main concepts and rules presented in Part I .
• It's the mutable state, stupid. [1]
All concurrency issues boil down to coordinating access to mutable state. The less
mutable state, the easier it is to ensure thread safety.
• Make fields final unless they need to be mutable.
• Immutable objects are automatically thread-safe.
Immutable objects simplify concurrent programming tremendously. They are sim-
pler and safer, and can be shared freely without locking or defensive copying.
• Encapsulation makes it practical to manage the complexity.
You could write a thread-safe program with all data stored in global variables, but