How to calculate memory usage of a Java program?

First calculate the memory used before your code execution i.e. first line of your code.

long beforeUsedMem=Runtime.getRuntime().totalMemory()-Runtime.getRuntime().freeMemory();

Calculate the memory used after your code execution:-

long afterUsedMem=Runtime.getRuntime().totalMemory()-Runtime.getRuntime().freeMemory();

Then you can do:

long actualMemUsed=afterUsedMem-beforeUsedMem;

It will give you actual memory utilized by your program.

For further memory analysis your best bet is any profiler tool like jvisualvm.

Do remember it, that Runtime.getRuntime().totalMemory(), this memory is total memory available to your JVM.
java -Xms512m -Xmx1024m , it means that total memory of your program will start with 512MB, which may lazily loaded to max of 1024MB.
So if you are running same program, on different JVMs, Runtime.getRuntime().totalMemory() might give you different results.

You can use top command in ubuntu to check % CPU use or % memory use while running the java programme.

top command will give you these many information.

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND

just type top and hit enter in your terminal & check java in command section.

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