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Message:

Re: look ! What's wrong with java in memory ?

Posted by Wil on August 26, 2001 at 9:01 PM

> try the following program, it will throw
> a out of memory exception when it get about
> no more than 10M memory. ( it require 32 M )
> what's wrong with java!!!

> class MType {
> int dummy;
> }
> public class MemTest {
> public static void main(String[] args) {
> int maxmsg = 8000000;
> MType[] msg = new MType[maxmsg];
> for(int i= 0; i< maxmsg; i++) {
> if( i % 1000 == 0)
> System.out.println(i);
> msg[i] = new MType();
> }
>
> }
> }
>

It is not 32MB. Objects require memory, not just the data inside I believe.

> MType[] msg = new MType[maxmsg];
This uses memory too?

Keep track of the memory free and used with Runtime.
When I tested it, it took roughly about 16 bytes (it differs) for each object.
so 16 * 8,000,000 = 128MB.

At the end of the Out of memory exception, Java used roughly about half (64M) of the total memory on my system.

Runtime rt = Runtime.getRuntime();

After each println (every 1,000 allocation), I put:
System.out.println("total mem:"+rt.totalMemory() );
System.out.println("free mem: "+rt.freeMemory() );