How does java implements runtime polymorphism.?

Question

Hi all.
we know how does runtime polymorphism take place in java.
But my quesions is , how does java implement it internally.
in C++, with the use of keyword virtual , complier decides to make a call at runtime using virtual table and Vptr.
like in c++,
class base {
public:
virtual void show(){
cout<<"I am in base class"<<endl;
class child : public base {
public:
void show(){
cout<<" I am in child class"<<endl;
int main(){
base*p = new child();
p->show();
return 0;
out put - I am in child class.
but if we remove the virtual keyword then output
I am in base class..
We know how it happens
but in java
class base {
void show(){
System.out.println("I am in base class");
class child extends base {
void show(){
System.out.println(" I am in child class");
class demo {
public static void main(string args[ ]){
base b;
child c = new child();
b = c;
b.show();
output is - I am in child class
but how can i bring the output as
I am in base class ---
complier knows that b is base reference so y doesnt it just use base version.

Answer 1

if all methods are virtual..then we should always have runtime binding but we do have early biding too.
shouldnt we able to call base verison using a base reference variable like in c++.
May be I m mixing big times java n c++. But it seems to me as core java is much like c++ . The things u can do in c++ , u can do same in java in different ways.