The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Dev.java for updated tutorials taking advantage of the latest releases.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

Concurrent Random Numbers

In JDK 7, java.util.concurrent includes a convenience class, ThreadLocalRandom, for applications that expect to use random numbers from multiple threads or ForkJoinTasks.

For concurrent access, using ThreadLocalRandom instead of Math.random() results in less contention and, ultimately, better performance.

All you need to do is call ThreadLocalRandom.current(), then call one of its methods to retrieve a random number. Here is one example:

int r = ThreadLocalRandom.current() .nextInt(4, 77);