Java OCA OCP Practice Question 1517

Question

Consider the following code: 

interface Pet{  } 
class Bird implements Pet  {  } 
class Eagle extends Bird  {  } 
class Bat  {  } /*  w w w . jav a  2  s .  co  m*/
public class Main  { 
     
    public static void main (String [] args)  { 
        Pet f = new Eagle (); 
        Eagle e = new Eagle (); 
        Bat b = new Bat (); 
         
        if (f instanceof Bird) System.out.println ("f is a Bird"); 
        if (e instanceof Pet) System.out.println ("e is a Pet"); 
        if (b instanceof Pet) System.out.println ("f is a Bird"); 
     } 
}

What will be printed when the above code is compiled and run?

Select 1 option

  • A. It will not compile.
  • B. It will throw an exception when run.
  • C. f is a Bird e is a Pet
  • D. f is a Bird
  • E. e is a Pet 


Correct Option is  : C

Note

Note that there is no compilation issue with b instanceof Pet because Pet is an interface and it is possible for b to point to an object of a class that is a sub class of Bat and also implements Pet.

So the compiler doesn't complain.

If you make Bat class as final, b instanceof Pet will not compile because the compiler knows that it is not possible for b to point to an object of a class that implements Pet.




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