Java's garbage collector has advanced from pure stop-the-world mark-and-sweep collection over the years. In Java 7, a new generational garbage collector became the default, working concurrently with application threads to minimize GC pauses and collection time on multicore systems. If you're curious, check out these resources about how it works:
Note also that the JRE ships with multiple garbage collectors that you can select manually, and that some of the collectors tune themselves to match the application.
* http://www.drdobbs.com/jvm/g1-javas-garbage-first-garbage-co...
* http://www.oracle.com/technetwork/java/javase/tech/g1-intro-...
Note also that the JRE ships with multiple garbage collectors that you can select manually, and that some of the collectors tune themselves to match the application.