OCA Java SE 8 Mock Exam - OCA Mock Question 21








Question

What is the output of the following code? 

class Base {
  String var = "Main";

  void printVar() {
    System.out.println(var);
  }
}

class Derived extends Base {
  String var = "AAA";

  void printVar() {
    System.out.println(var);
  }
}

class Main {
  public static void main(String[] args) {
    Base base = new Base();
    Base derived = new Derived();

    System.out.println(base.var);
    System.out.println(derived.var);
    base.printVar();
    derived.printVar();
  }
}

    
    a  Main 
       Main 
       Main 
       AAA 

    b  Main 
       AAA 
       Main 
       AAA 

    c  Main 
       Main 
       Main 
       Main 

    d  Main 
       AAA 
       AAA 
       AAA




Answer



A

Note

The following line of code refers to an object of the class Base, using a reference variable of type Base. Hence, both of the following lines of code print Main: 

System.out.println(base.var); 
base.printVar();

The following line of code refers to an object of the class Derived using a reference variable of type Base: 

Base derived = new Derived();

Because the instance variables bind at compile time, the following line accesses and prints the value of the instance variable defined in the class Base: 

System.out.println(derived.var);    // prints Main

In derived.printVar(), the method printVar is called using a reference of type Base, invoking on a Derived object and so executes the overridden printVar method in the class Derived. 

class Base {//from w  ww .  j  av a  2 s  . c  o m
  String var = "Main";

  void printVar() {
    System.out.println(var);
  }
}

class Derived extends Base {
  String var = "AAA";

  void printVar() {
    System.out.println(var);
  }
}

class Main {
  public static void main(String[] args) {
    Base base = new Base();
    Base derived = new Derived();

    System.out.println(base.var);
    System.out.println(derived.var);
    base.printVar();
    derived.printVar();
  }
}