Hi Friend,

The run-time polymorphism is basically the Method Overriding.Here super class reference is referring to subclass object and compiler does not know which method to call.

For ex:
class Flower {
void which() {
System.out.println("A Beautiful flower.");
}
}
class Rose extends Flower {
void which() {
System.out.println("Rose");
}
}
class Lotus extends Flower {
void which() {
System.out.println("Lotus.");
}
}
class RuntimePolymorphism {

public static void main(String[] args) {
Flower ref1 = new Flower();
Rose ref2 = new Rose();
Lotus ref3 = new Lotus();
ref1.which();
ref2.which();
ref3.which();
}
}

For more information,please visit the following links:

http://www.roseindia.net/java/master-java/method_overriding.shtml
http://www.roseindia.net/java/javascript-array/modified-java-method-overriding.shtml

Thanks