Java OCA OCP Practice Question 1118

Question

What will the following program print when compiled and run? 

class MyClass{ //from ww  w. ja v a2s.c  om
  public void play () throws Exception{ 
    System.out.println ("Playing..."); 
   } 
} 

public class MySubClass extends MyClass{ 
   public void play (){ 
      System.out.println ("Playing MySubClass...");       
    } 
   public static void main (String [] args){ 
       MyClass g = new MySubClass (); 
       g.play (); 
    } 
}

Select 1 option

  • A. It will not compile.
  • B. It will throw an Exception at runtime.
  • C. Playing MySubClass...
  • D. Playing...
  • E. None of these. 


Correct Option is  : A

Note

Observe that play() in MyClass declares Exception in its throws clause.

class MySubClass overrides the play() method without any throws clause.

This is valid because a list of no exception is a valid subset of a list of exceptions thrown by the superclass method.

Now, even though the actual object referred to by 'g' is of class MySubClass, the class of the variable g is of class MyClass.

At compile time, compiler assumes that g.play() might throw an exception, because MyClass's play method declares it, and thus expects this call to be either wrapped in a try-catch or the main method to have a throws clause for the main() method.




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