Predict the output of following Java Programs:
Question 1
// file name: Main.java class Base { protected void foo() {}} class Derived extends Base { void foo() {}} public class Main { public static void main(String args[]) { Derived d = new Derived(); d.foo(); }} |
Output: Compiler Error
foo() is protected in Base and default in Derived. Default access is more restrictive. When a derived class overrides a base class function, more restrictive access can’t be given to the overridden function. If we make foo() public, then the program works fine without any error. The behavior in C++ is different. C++ allows to give more restrictive access to derived class methods.
Question 2
// file name: Main.java class Complex { private double re, im; public String toString() { return "(" + re + " + " + im + "i)"; } Complex(Complex c) { re = c.re; im = c.im; }} public class Main { public static void main(String[] args) { Complex c1 = new Complex(); Complex c2 = new Complex(c1); System.out.println(c2); }} |
Output: Compiler Error in line “Complex c1 = new Complex();”
In Java, if we write our own copy constructor or parameterized constructor, then compiler doesn’t create the default constructor. This behavior is same as C++.
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