How Does Default Virtual Behavior Differ in C++ and Java?
Let us discuss how the default virtual behavior of methods is opposite in C++ and Java. It is very important to remember that in the C++ language class member methods are non-virtual by default. They can be made virtual by using virtual keywords. For example, Base::show() is non-virtual in following program and program prints “Base::show() called”.
Example:
CPP
// C++ Program to Illustrate How // Default Virtual Behave // Different in C++ and Java // Importing required libraries // Input output stream #include <iostream> using namespace std; // Class 1 // Superclass class Base { // Granting public access via // public access modifier public : // In c++, non-virtual by default // Method of superclass void show() { // Print statement cout << "Base::show() called" ; } }; // Class 2 // Subclass class Derived : public Base { // Granting public access via public access modifier public : // Method of subclass void show() { // Print statement cout << "Derived::show() called" ; } }; // Main driver method int main() { // Creating object of subclass Derived d; // Creating object of subclass // with different reference Base& b = d; // Calling show() method over // Superclass object b.show(); getchar (); return 0; } |
Output:
Base::show() called
Output Explanation: Adding virtual before definition of Base::show() makes program print “Derived::show() called”. In Java, methods are virtual by default and can be made non-virtual by using the final keyword. For example, in the following java program, show() is by default virtual and the program prints “Derived::show() called“.
Let us see what happens in the case we use the same concept in a java programming language via the example proposed below.
Example:
Java
// Java Program to Illustrate // How Default Virtual Behave // Different in C++ and Java // Importing required classes import java.util.*; // Class 1 // Helper class class Base { // Method of sub class // In java, virtual by default public void show() { // Print statement System.out.println( "Base::show() called" ); } } // Class 2 // Helper class extending Class 1 class Derived extends Base { // Method public void show() { // Print statement System.out.println( "Derived::show() called" ); } } // Class 3 // Main class public class GFG { // Main driver method public static void main(String[] args) { // Creating object of superclass with // reference to subclass object Base b = new Derived(); ; // Calling show() method over Superclass object b.show(); } } |
Derived::show() called
Note: Unlike C++ non-virtual behavior, if we add final before the definition of the show() in Base, then the above program fails in the compilation.