To the extent I understand it, a java object at runtime has a jump table for its methods; which method actually gets called depends on the inheritance hieararchy. You define your own class A to extend Object, and then B to extend A; any object of any of the three classes has an entry in its jump table for, say, toString(). If you've defined toString in A, then objects of type A have a pointer to toString() in A's definition; if you do not define toString in B, then the jump table for an object of type B ALSO has a pointer to toString() in A's definition, and so forth.
When I looked at this some years ago, one difference between java and C++ was that C++ had a separate table for non-virtual methods. Java doesn't have non-virtual methods; any public method can be overridden (well, except for final, which is a compile-time animal. Let's leave final out of this).
Anyway. I don't know if that's what you were looking for, but more detail really should come from longer articles than the forum is liable to support, at least as a reply...
Thanks Ralph. I'm certainly looking at much more than this.that is how internal implementation of method call happens. I understand that all non-final methods by default are like virtual methods in Java. I wanted to see how parentRef=ChildObj denies to call a pure child method, the real tracing by JVM to implement method invocation.