Java Has Memory Leaks

When C/C++ programmers refer to memory leaks in Java, they probably don't understand how Java works. Java doesn't offer pointer arithmetic; typical C-style memory leaks, such as out-of-bounds array accesses, are caught by the Java compiler.

However, these programmers may mean that objects that are no longer needed by the program are not being garbage collected. This becomes an issue if the program keeps creating new objects and requiring more memory, and eventually crashes when the maximum memory allocation is exceeded.

This kind of problem is a consequence of bad programming style, since the garbage collector can only do its job when an object is completely dereferenced, meaning the program no longer refers to the object. A good profiling tool, such as JProfiler (http://www.ej-technologies.com/products/jprofiler/overview.html), can help identify code using excessive amounts of memory.

JProfiler is a commercial product; many open source profilers are listed at http://java-source.net/.

Another memory-related complaint is that the Java garbage collector is executing at poorly timed intervals, causing the application to halt for seconds as the collector sweeps and cleans. The Java Virtual Machine (JVM) comes with several different garbage collectors, which collect in various ways and can be selected and fine-tuned from the command line. Information on the performance of the chosen collector can be gathered and analyzed. A good hands-on explanation of this topic, centered around the JTune visualization tool, can be found at http://www-106.ibm.com/developerworks/java/library/j-perf06304/. Another possibility is GC Portal (http://java.sun.com/developer/technicalArticles/Programming/GCPortal/).