How to verify memory leak in Java

Question

From the question Creating a memory leak with Java there are many ways to create memory leaks in Java, but I am just trying to create a simple memory leak and being able to observe its effect somehow. In fact, after trying to create a memory leak I would like to verify that ( in numbers or something) so that I assure that the memory leak has been successfully created. Can we investigate the occurrence of memory leak in our code by not using a third party application, just by inserting e.g. runtime.maxMemory() in our code?

Answer 1

This is a poor-man's substitute for a memory profiling tool:

public static long bytesOccupied() {
   final Runtime rt = Runtime.getRuntime();
   for (int i = 0; i < 2; i++) rt.gc();
   return rt.totalMemory()-rt.freeMemory();
}

I have used this on several occasions and can attest that it works at least on some setups. Try it and see if it gives sensible results for you.

Otherwise, it is really easy to start VisualVM, which is already installed on your computer with the JDK. Be sure to install the optional VisualGC plugin. Make your code do some allocations in a loop and watch the GC generations churn. Use a short sampling time (100 or 200 ms) to get a realtime feel.