java stream API is really cool addition to the java language (if you are a c++ hardcore fan please pass on this post :) ) i have tried to solve this problem and i tried multiple submission just to try out java stream API ... that submission was successful but this one wasn't and the only change is return a.parallelStream().allMatch(e -> e == a.get(0)); which was resulted in failure ... can anyone explain why e == a.get(0) didn't work but int c = a.get(0) and e == c did work ?