In Java streams is peek really only for debugging?

Question

I\'m reading up about Java streams and discovering new things as I go along. One of the new things I found was the peek() function. Almost everything I\'ve read

Answer 1

Perhaps a rule of thumb should be that if you do use peek outside the "debug" scenario, you should only do so if you're sure of what the terminating and intermediate filtering conditions are. For example:

return list.stream().map(foo->foo.getBar())
                    .peek(bar->bar.publish("HELLO"))
                    .collect(Collectors.toList());

seems to be a valid case where you want, in one operation to transform all Foos to Bars and tell them all hello.

Seems more efficient and elegant than something like:

List bars = list.stream().map(foo->foo.getBar()).collect(Collectors.toList());
bars.forEach(bar->bar.publish("HELLO"));
return bars;

and you don't end up iterating a collection twice.