Output of Java Program | Set 4


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();

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);

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++.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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