shrink a few lines of repeated code.

[Willie Tsang]

This is one method from Hashset Iterator. it returns the next object from the current one. I have a NullPointerException while running "if(current==null|current.next==null)" so I added the try and catch and it works. First question is, why am i getting the nullpointer exception if i have previously checked hasNext(). 2nd question, since the catch{} has the same code in the try{}, is it possilbe to strink some of the catch{}? Many Thanks.

public Object next(){
			previous=current;
			previousBucket=bucket;
			try{	
				if(current==null|current.next==null){
					bucket++;
					while(bucket<buckets.length&&buckets[bucket]==null)
						bucket++;
					if(bucket<buckets.length)
						current=buckets[bucket];
					else
						throw new NoSuchElementException();
				}
				else
					current=current.next;
			}
			catch(NullPointerException e){
				bucket++;
				while(bucket<buckets.length&&buckets[bucket]==null)
					bucket++;
				if(bucket<buckets.length)
					current=buckets[bucket];
				else
					throw new NoSuchElementException();
				}
			return current.data;
		}

[William P O'Sullivan]

What line in the above code caused the NPE?

WP

[Willie Tsang]

eclipse said "if(current==null|current.next==null)"

[Paul Clapham]

Aha! Change this line of code from

if(current==null|current.next==null){

to

if(current==null||current.next==null){

Why? The "|" operator always evaluates both of its operands: so even if current == null is true, it will still look at current.next == true, thus throwing the NPE for current.next. Whereas the "||" operator will only evaluate its RHS if its LHS is false. The latter is what you want in this case, and frankly in almost every case.

And don't ever respond to NPE by writing code which catches it. A NullPointerException always indicates a programming error which should be found and fixed, rather than ignored and worked around.

(Of course when I say "don't ever" and "always" there, there are always exceptions to such things. But if it's your code, that isn't one of the exceptions.)

[Willie Tsang]

Thanks alot, that was a clear explainion. and thanks for the advice.