Finding Memory Usage in Java

Question

Following is the scenario i need to solve. I have struck with two solutions.

I need to maintain a cache of data fetched from database to be shown on a Swing GUI. Wheneve

Answer 1

Just a side note: Runtime.freeMemory() doesn't state the amount of memory that's left of allocating, it's just the amount of memory that's free within the currently allocated memory (which is initially smaller than the maximum memory the VM is configured to use), but grows over time.

When starting a VM, the max memory (Runtime.maxMemory()) just defines the upper limit of memory that the VM may allocate (configurable using the -Xmx VM option). The total memory (Runtime.totalMemory()) is the initial size of the memory allocated for the VM process (configurable using the -Xms VM option), and will dynamically grow every time you allocate more than the currently free portion of it (Runtime.freeMemory()), until it reaches the max memory.

The metric you're interested in is the memory available for further allocation:

long usableFreeMemory= Runtime.getRuntime().maxMemory()
    -Runtime.getRuntime().totalMemory()
    +Runtime.getRuntime().freeMemory()

or:

double usedPercent=(double)(Runtime.getRuntime().totalMemory()
    -Runtime.getRuntime().freeMemory())/Runtime.getRuntime().maxMemory()