How to Determine an Objects Size ?

[Faisal Khan]

I need to know that how can i determine the actual size occupied by an object in memory.Either via any method specified in Java API or any implementation by JVM.

[Cindy Glass]

They were just talking about an objects size in Beginner yesterday.
You might try using the search link at under the two buttons above. There have been LOTS of conversations on this topic in Beginner as well as Intermediate.

[Thomas Smets]

Have you already tried to simply look at the long freeMemory() or long totalMemory() &see how you could use these ?
Say doing smthg like :

 
package test.lang;
public class ObjectSize
{
  public static final int NBR_OBJ = 100000;
/** 
  * This code is copyleft without any restriction.
  * Mentionning the author is just nice for him !
  * @author <a href="[e-mail]">Thomas SMETS</a>
  */
  public static void main (String[] args)
  {
    Runtime rt;
    long freeMemoryBefore = (rt =Runtime.getRuntime ()).freeMemory (), memUsed;
    Object[] o= new Object[NBR_OBJ];
    for (int i = 0; i < NBR_OBJ; i++) 
      o[i] = new Object();
    System.out.println ("Memory used is : " 
                        + (memUsed = freeMemoryBefore - rt.freeMemory () ) );
    System.out.println ("Average size is : " + (memUsed / NBR_OBJ) + " bytes");                        
    
    for (int i = 0; i < NBR_OBJ; i++) 
      o[i] = null;;
  }
}

Running the program gives :

Memory used is : 1130416
Average size is : 11 bytes
Press any key to continue...

Changing the line to

 
  public static final int NBR_OBJ = 1000000; 

Ten times more objects gives :

Memory used is : -4076792
Average size is : -4 bytes
Press any key to continue...

Hope this helps !