How to solve OutOfMemoryError?

Question

For a project for school I have to program different kind of algorithms. The problem is, I got a working algorithm. But I have to run it several times and after some time it gives me the following errors:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

I know what the error means, but is it possible to let Java search for empty space during the run? I know it uses a lot of space which isn't used at some point. It sets a lot of object to null during the application run and create a lot of new ones, because of this it runs out of memory.

So concrete: is it possible to let the JVM free some space that is set to null? Or free some space in the time the program is running? I know I can set the JVM to more space, but sooner or later I will run to the same problem.

If you need my IDE (in case it is IDE specific) it is Eclipse.

Answer 1

Please google 'garbage collection'. Java is always looking to reuse space from objects that you aren't using. If you run out of memory, you either need to use -Xmx to configure for more memory, or you have to fix your code to retain fewer objects. You may find that a profiler like jvisualvm would help you find wasteful memory usage.

Answer 2

If you're using an Oracle/Sun JVM, I'd recommend that you download Visual VM 1.3.3, install all the plugins, and start it up. It'll show you what's happening in every heap generation, threads, CPU, objects, etc. It can tell you which class is taking up the most heap space.

You'll figure it out quickly if you have data.