If you load 2 classes with custom classloader, the output of jmap -permstat shows 3 classes for this class loader:

Attaching to process ID 25522, please wait...
Debugger attached successfully.
Client compiler detected.
JVM version is 12.0-b01-fastdebug
586 intern Strings occupying 34032 bytes.
finding class loader instances ..done.
computing per loader stat ..done.
please wait.. computing liveness.................................................done.
class_loader classes bytes parent_loader alive? type

<bootstrap> 317 891720 null live <internal>
0xadb72d18 0 0 null live sun/misc/Launcher$ExtClassLoader@0xb1c97550
0xadb82248 3 3208 0xadb7b320 live java/net/URLClassLoader@0xb1c972a8
0xadb7b320 11 74328 0xadb72d18 live sun/misc/Launcher$AppClassLoader@0xb1ce0610

total = 4 331 969256 N/A alive=4, dead=0 N/A


===
import java.net.*;
import java.io.*;

public class ClassLoading {
        public static void main(String[] args) throws Exception {
                String dir = new File(".").getCanonicalPath();
                URLClassLoader loader = new URLClassLoader(new URL[] { new URL("file://" + dir + "/a.jar") });
                Class a = loader.loadClass("A");
                Class b = loader.loadClass("B");
                Thread.sleep(10000000);
        }
}
===