Studying garbage collection

The Java run-time system performs garbage collection automatically. It finds memory that a program is no longer using and frees it.

Garbage collection can only be run if the process is active. It is available from Package Statistics view, Class Statistics view and, when instance level information is collected, Instance Statistics view.

To view details about garbage collection, follow these steps.

In the Profiling Monitor view, select the monitor or agent. Right click, then select Open With > Package Statistics. The Package Statistics view opens.
Ensure that the Live Instances and Collected columns are visible. If they are not, right click, select Choose Columns, then set these columns to be visible.
See the results:
- In the Live Instances column, you can see how many instances for the current packages are still alive, not garbage collected.
- In the Collected column, you can see how many instances for the current packages are garbage collected.
- You can expand the current package to see the same information at the class level or open the Class Statistics view.
- You can also drill down at the instance level using Instance Statistics view, but only when you have collected instance level information. (To collect instance level information, select the Show Instance Level Information profiling option before launching or attaching to the profiled application.)
Click Run Garbage Collection and then Refresh Views . Notice the changes in the number of active instances and garbage collected, at the package or class level.
If you create a dump of the object references using the Collect Object References button , the instances at which you collected the object references will be indicated in the GC thread and marked by the numbered generations.