Determining Java Usage

Question

Hmmm. Is there any tutorial on memory usage in Java? I would have thought that Sun or IBM would have a good article on this subject, but I can not find anything that would look very solid. I am interested to know two things:

• at runtime, figuring out how much memory the classes in my package are currently using
• during development, evaluating the general utility memory requirements for various things, such as:
  • how much memory overhead is required for an empty object (in addition to the space required by its fields)
  • how much memory overhead is required when creating closures
  • how much memory overhead is required for collections like ArrayList

I can have hundreds of thousands of objects created, and I want to be a "good neighbor" so as not to waste RAM too much. I mean, I don’t care if I use 10% more memory than the “best case” (whatever that may be), but if I implement something that uses as much memory as possible 5 times, if I made a simple change, I would like to use less memory (or be able to create more objects for a fixed amount of available memory).

I found several articles ( Java Specialist Newsletter and something from Javaworld ) and one of the built-in classes java.lang.instrument.getObjectSize () that claims to measure the “approximation” (??) of memory usage, but they all seem vague ...

(and yes, I understand that a JVM running on two different operating systems can probably use different amounts of memory for different objects)

Answer 1

I used JProfiler a few years ago, and it did a good job, and you can break the memory usage to a rather granular level.

Answer 2

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