Compute memory required to allocated objects

I would like to compare memory usage, to allocate Calendar object and Joda's DateTime object.

// How much memory required to allocate 100 Calendar objects?
for (int i = 0; i < 100; i++) {
    Calendar c = Calendar.getInstance();
    l = l + c.getTimeInMillis();
    CalendarList.add(c);
}

// How much memory required to allocate开发者_StackOverflow中文版 Joda TimeDate objects?
for (int i = 0; i < 100; i++) {
    DateTime dateTime = new DateTime();
    l = l + dateTime.getMillis();
    DateTimeList.add(dateTime);
}

May I know is there any code I can add in to measure?

Use instrumentation to get an hint of memory usage:

public class MemUsage {

    public static void main(String[] args) {
        Instrumentation instr = InstrumentationAgent.getInstrumentation();
        if (instr == null) {
            System.err.println("No Instrumentation, use the VM option \"-javaagent:Instrumentation.jar\"");
            return;
        }
        System.out.println();
        System.out.println("an implementation-specific approximation of the amount of storage");
        System.out.println("Calendar = " + instr.getObjectSize(Calendar.getInstance()));
        System.out.println();
    }
}

Other option: MemoryMXBean but I never used that.

You could use the Java visual vm tool, there you can see what objects take what memory. I don't think there is a "in code" solution that is correct in all cases with a few lines of code.

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