Mock Question Doubt...EQ+..Operators and Assignment

[Hardik Raja]

Hello Friends,

Question ID : com.enthuware.ets.scjp.v5.2.185

The following class will print '2' when compiled and run.
 
class Test
{
   public static int[ ] getArray() {  return null;  }
   public static void main(String[] args)
   {
      int index = 1;
      try
      {
         getArray()[index=2]++;
      }
      catch (Exception e){  }  //empty catch
      System.out.println("index = " + index);
   }
}

Please select 1 option

A. True
B. False

The answer is A..

I have executed and seen that it prints 2...but I am not getting it..

I dont know why NullPointerException is not thrown at this loc..

getArray()[index=2]++;

here getArray() returns null after that index is set to 2..then when postfix increment operator is applied, why doesn't it throw a nullPointerException??

Can anyone please give their suggestions on the above problem.Thank you in advance.

Regards,
Hardik.S.Raja

[Paul Anilprem]

Hi Hardik,
There is an explanation given with it -

If the array reference expression produces null instead of a reference to an array, then a NullPointerException is thrown at runtime, but only after all parts of the array reference expression have been evaluated and only if these evaluations completed normally. The embedded assignment of 2 to index occurs before the check for a null pointer.

So NPE is thrown (put e.printStackTrace() or something in the empty catch block) but by then index has already been assigned the value of 2.

[Hardik Raja]

Hello Paul,

Got it..

Thanks
Hardik

[Anita Singh]

Hi,
NullPointerException is thrown here,but you are printing that exception.
make some change in your code:

public class PracticeTest {
public static int[ ] getArray() { return null; }
public static void main(String[] args)
{
int index = 1;
try
{
getArray() [index=2]++;
} catch (Exception e)
{
System.out.println(e);//change
}
System.out.println("index = " + index);
}
}
Now you will see that your program is throwing NullPointerException.