A possible wrong answer in ExamLab?

[Jennifer Zhen]

Hello, I found in the Practice exam 1, the 41th question:

  public class Testing {
	    public static void main(String... args)
	    {	
	    	
	    	A ab = new B();
	    	ab.blast();
	    

	    }

}

class B extends A {
	
	public void blast() throws NumberFormatException
	{ throw new NumberFormatException();
	
	}
}
class A {
		
	public void blast() throws InterruptedException
	{
		throw new InterruptedException();
	}
	

}  

the answer is the result of the program would be throwing (runtime) NumberFormatException. But I figured since A is the superclass, when you call B with A ref, the compliler got check if the checked exception is handled. And it's true that when I tested in a real IDE, a complier error happened.

[Narendhiran Nagarajan]

NumberFormatException and InterruptedException are Unchecked (Runtime) Exceptions.
When you override a method, you can declare any Unchecked exception.But the checked exceptions cannot be new or broader than the overridden method.

[Sridhar Gudipalli]

I have not looked into the actual question. But, if ab.blast() would surround with try/catch, then the answer (runtime exception) would be correct.
Either it is typo in question or missed the "compile time error" option in solution(s).

try {
ab.blast();
}
catch (InterruptedException e) {
e.printStackTrace();
}

[Henry Wong]

Narendhiran Nagarajan wrote:NumberFormatException and InterruptedException are Unchecked (Runtime) Exceptions.

InterrruptedException is a checked exception -- and Jennifer is correct in that the compiler should complain.

Henry

[Devaka Cooray]

Jennifer

Nice subject line. But the code you posted here is not exactly from ExamLab. It seems you edited the code. In the ExamLab question, there is a "throws" declaration for the main method, so there are no error at compile time. In ExamLab, there is a "Copy Program" button, so you can easily copy and paste the code here.

This is the exact code:

class A{
          public void blast()throws InterruptedException{
               throw new InterruptedException();
          }
     }

     class B extends A{
          public void blast()throws NumberFormatException{
               throw new NumberFormatException();
          }
     }
     
     public class Experr{
          public static void main(String args[])throws Exception{
               A ab=new B();
               ab.blast();
               System.out.println("Done");
          }
     }

[Narendhiran Nagarajan]

Sorry for giving wrong info.

Eventhough Interrupted Exception is a checked exception, it will not create a problem.
As I said early
"When you override a method, you can declare any Unchecked exception.But the checked exceptions cannot be new or broader than the overridden method. "
I would like to add that-
"Unless its needed, the overriding method doesnt have to declare all the Checked Exceptions, what the overridden method have."

So, b.blast() doesnt have to declare the InterruptedException or its subtype.

[Jennifer Zhen]

Hi Devaka,

I'm sorry for the subject line, but I was puzzled at the first place, that was true. Yes, you were right, I could have copied and pasted the code, but on my ThinkPad T40, which I am not sure why the resolution is not right when running ExamLab so I had to installed it on a separate slower machine, which I don't have IDEs.

Yes, you are right. If the throw clause is added to the main function, then it is fine.

Thanks for the clarifying.

Devaka Cooray wrote:Jennifer

Nice subject line. But the code you posted here is not exactly from ExamLab. It seems you edited the code. In the ExamLab question, there is a "throws" declaration for the main method, so there are no error at compile time. In ExamLab, there is a "Copy Program" button, so you can easily copy and paste the code here.

This is the exact code:

class A{
          public void blast()throws InterruptedException{
               throw new InterruptedException();
          }
     }

     class B extends A{
          public void blast()throws NumberFormatException{
               throw new NumberFormatException();
          }
     }
     
     public class Experr{
          public static void main(String args[])throws Exception{
               A ab=new B();
               ab.blast();
               System.out.println("Done");
          }
     }

[Devaka Cooray]

Jennifer Zhen wrote:I'm sorry for the subject line,

No I meant that this subject line is really good , because it makes me to read this topic. So, if there are any errors, I can figure them out and fix them.