OpenJDK JRE vs HotSpot JVM? ObjectSizeCalculator only works with HotSpot

Question

There is a class in the java ext classes that computes object sizes but it only works with the HotSpot JVM.  jdk.nashorn.internal.ir.debug.ObjectSizeCalculator  
  https://stackoverflow.com/a/39406536  
  https://stackoverflow.com/questions/52353/in-java-what-is-the-best-way-to-determine-the-size-of-an-object#comment84178865_39406536  
  
What is the status of HotSpot?  It took me a while to figure out that the error mesage was due to the JVM version:  
  java.lang.NoClassDefFoundError: Could not initialize class jdk.nashorn.internal.ir.debug.ObjectSizeCalculator$CurrentLayout  
  
This would be very useful with spark RDDs during debug...

Answer

I'm still curious about HotSpot but a different way to solve this is something like this using openjdk jol project:

```
import org.openjdk.jol

val l = List(1,2,3)

// Convert Any into AnyRef: https://stackoverflow.com/a/23892913
val jo = l.asInstanceOf[AnyRef]
val gl = jol.info.GraphLayout.parseInstance(jo)
gl.totalSize()
```

OpenJDK JRE vs HotSpot JVM? ObjectSizeCalculator only works with HotSpot

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