How to detect memory leak in java?

Question

My doubt is that doesn't Java virtual machine have a garbage collector that will collect and free all unreferenced memory automatically?

Answer 1

you may want to check out jconsole. It's also part of the JDK and I have found it helpful to find emory/reference leaks in conjunction with jhat. Also take a look at this blog http://blog.emptyway.com/2007/04/02/finding-memory-leaks-in-java-apps/

Answer 2

I suggest you use visualvm that comes with JDK 5 onwards.

If your code creates an object and has more than 3 level of reference of it or if Java garbage collector algorithm thinks that this object may be referenced by any your code than it is not garbage collected.
therefore it becomes memory leak.

Where do these occurs in java code?
Most vulnerable code in Static class, singleton class or static methods where you want instance object to be alive in multiple condition/scenario for unknown time in objects life cycle, may result into object left over (read stay in memory without any further use) and GC unable to decide if it can be GC'ed. Therefore memory leak.

Answer 3

There is no sure sort answer but you can use profile and memory dump to find memory leak in Java. JConsole can also help to provide graph of memory usage which can show pattern for memory leak.