In Java, how do I find out what is my maximum heap size?

Question

I have the following class in Java :

public class MemoryUsage 
{
    public static void main(String[] args)
    {
        Vector v = new Vector();
        while (true)
        {
            byte b[] = new byte[1048576];

            try {
                Thread.sleep(200);
            } catch (InterruptedException ie){}        
            v.add(b);
            Runtime rt = Runtime.getRuntime();
            System.out.println( "free memory: " + rt.freeMemory() );
        }
    }

    public void showCurrentTime() 
    {
        long time = System.currentTimeMillis();
        System.out.println(time);   
    } 
}

And I want to limit how much memory can be used by this program. I tried to set an initial and maximum size (from command-line), like follows :

C:\JMX_code\Memory_test>java -Xms2m -Xmx4068M MemoryUsage
Error occurred during initialization of VM
The size of the object heap + VM data exceeds the maximum representable size

But this doesn't work. How do I figure out what is my own maximum heap size ?

My Java version info. is as follows :

Java(TM) SE Runtime Environment (build 1.7.0_02-b13) Java HotSpot(TM) 64-Bit Server VM (build 22.0-b10, mixed mode)

How much RAM is on your machine and which version of Java are you running? — Ishmael, Mar 21 '16 at 16:02
@Coffee what is your RAM + swap memory size? I doubt if it is less than 4gb. Can you try with -Xmx =2048m. — Madhusudana Reddy Sunnapu, Mar 21 '16 at 16:08
Which version of Java are you running (including whether it is 32 or 64 bit) and what platform are you running on? — callyalater, Mar 21 '16 at 16:14
[This question](http://stackoverflow.com/questions/461260/is-there-a-maximum-number-you-can-set-xmx-to-when-trying-to-increase-jvm-memory) might be related. — callyalater, Mar 21 '16 at 16:42
You may need to specify `-d64` on the command line to force the JVM to accept the specified heap size. [This site](http://javarevisited.blogspot.com/2012/12/invalid-initial-and-maximum-heap-size.html) explains some of these heap problems. — callyalater, Mar 21 '16 at 16:51
@callyalater - not sure why, but this works fine on my Mac, ... just not on Windows — Caffeinated, Mar 22 '16 at 16:51
@MadhusudanaReddySunnapu - not sure why, but this works fine on my Mac, ... just not on Windows — Caffeinated, Mar 22 '16 at 16:51

score 1 · Answer 1 · edited Mar 21 '16 at 19:43

1

Try changing it to:

-Xms2034M -Xmx4068M MemoryUsage

edited Mar 21 '16 at 19:43

Andy

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answered Mar 21 '16 at 19:36

Ishmael

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In Java, how do I find out what is my maximum heap size?

1 Answers1