Pauses

Modern versions of the JDK really do have truly exceptional GC performance. Java 7 will feature a compacting, predictable delay time GC system that can take excellent advantage of many-core systems to provide great throughput.

With GC systems, there's a trade-off between speed of collection, CPU efficiency, and overall memory usage. Java allows these parameters to be tuned for a specific use case, but it is true that the default configuration tends to emphasize CPU efficiency over overall memory usage.