I also had this question when I was playing with DefaultTuple once. I
removed that null-addition loop, but then it failed while setting an object
at an specific index. There is a code in Pig which sets value at a specific
index in the tuple, which will throw NPE if you dont first add null in the
list. This is one of those oddities of java.
List<String> list = new ArrayList<String>(3);
list.set(1,"mystring");
throws NPE, while following doesn't.
List<String> list = new ArrayList<String>(3);
for (int i =0; i < 3; i++) {
list.add(null);
}
list.set(1,"mystring");
Since client code using DefaultTuple is permissible to set value at any
index of tuple, we have no choice but to null-fill the list first.
Hope it helps,
Ashutosh
On Sat, May 26, 2012 at 9:13 PM, Jonathan Coveney <jcove...@gmail.com>wrote:
> -user
> +dev
>
> Haha, I made this very same comment somewhere, and noticed the exact same
> thing (I think I mention it in my SchemaTuple benchmarking).
>
> The reason is so that tuple.size() will return the right value. Also, the
> expectation is that if you append, it goes to the end of all of the nulls,
> not the first position. It's a little confusing, and yeah, it surprised me
> too.
>
> You could definitely amortize the cost of creation over the sets that the
> user does by keeping an index, but when I first saw it I decided that the
> (slightly) increased memory footprint and the increase in code complexity
> wasn't worth a very minimal increase.
>
> 2012/5/26 Prashant Kommireddi <prash1...@gmail.com>
>
> > I rambled across this while reviewing one of Jon's patches. Here is the
> > code from DefaultTuple
> >
> > /**
> > * Construct a tuple with a known number of fields. Package level so
> > that callers cannot directly invoke it.
> > * <br>Resulting tuple is filled pre-filled with null elements. Time
> > complexity: O(N), after allocation
> > *
> > * @param size
> > * Number of fields to allocate in the tuple.
> > */
> > DefaultTuple(int size) {
> > mFields = new ArrayList<Object>(size);
> > for (int i = 0; i < size; i++)
> > mFields.add(null);
> > }
> >
> >
> > Why are we walking through the list to add nulls? Wouldn't the initial
> > creation of ArrayList suffice?
> > mFields = new ArrayList<Object>(size) should be enough.
> >
> > Thanks,
> > Prashant
> >
>
