Java OCA OCP Practice Question 1911

Question

Which statements, when inserted at line 1, will cause an exception at run time? 


class MyClass  {}
class MyClass1 extends MyClass  {}
class MyClass2 extends MyClass  {}

public class Main{
  public static void main (String args []){
     MyClass b = new MyClass ();
     MyClass1 b1 = new MyClass1 ();
     MyClass2 b2 = new MyClass2 ();
     // insert statement here
   }/*from  w ww .j ava2 s.c  o  m*/
}

Select 1 option

  • A. b = b1;
  • B. b2 = b;
  • C. b1 = (MyClass1) b;
  • D. b2 = (MyClass2) b1;
  • E. b1 = (MyClass) b1;


Correct Option is  : C

Note

For A.

There won't be a problem anytime because MyClass1 is a MyClass

For B.

It fails at Compile time as an object referenced by b may not be a MyClass2, so an explicit cast will be needed.

For C.

It will pass at compile time but fail at run time as the actual object referenced by b is not a MyClass1.

For D.

It will not compile because b 1 can never point to an object of class MyClass2.

For E.

This won't compile. Another cast is needed. i.e. b1 = (MyClass1)(MyClass)b1;




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