Clojure has strong Java interoperability and underpinning, due to which programmers can leverage the performance benefits nearing those of Java. For performance-critical code, it is sometimes necessary to understand how Clojure interacts with Java and how to turn the right knobs. Numerics is a key area where Java interoperability is required to get optimum performance. Type hints are another important performance trick that is frequently useful. There are several open source Clojure libraries that make such activities easier for the programmer.

In the next chapter, we will dig deeper below Java and see how the hardware and the JVM stack play a key role in offering the performance we get, what their constraints are, and how to use their understanding to get better performance.