Both codes have behavior that throws an exception if the value doesn't exist.

Optional<FreePosts> byId = Optional.ofNullable(freePostsRepository.findById(id))
                .orElseThrow(NoSuchElementException::new);

FreePosts byId = freePostsRepository.findById(id)
                .orElseThrow(NoSuchElementException::new);

I would like to know the difference between the two codes.

CodePudding user response：

Both codes have behavior that throws an exception if the value doesn't exist.

In fact, that is not true. They don't both behave that way.

One of those two versions is incorrect, but which one it is depends on the declared return type of findById is.

• If the return type is FreePosts, then the second version does not compile, and it is therefore incorrect.

  The first version is equivalent to this:

   FreePosts byId = freePostsRepository.findById(id);
   if (byId == null) {
       throw new NoSuchElementException();
   }
  

  In my opinion, it would be better to write an explicit throw in this case, not least because you can include a message.

• If the return type Optional<FreePost> then the second version is correct¹.

  In this case, the first version is going to throw an exception if and only if findById returns a null. But if findById is written correctly, it won't ever return null. (Instead, if should return an empty Optional<FreePosts> instance.) So:

  • If findById doesn't have a bug that causes it to return null, the first version is not going to throw a NoSuchElementException, and therefore the ofNullable(...) and the orElseThrow(...) are pointless.

  • If there is a bug in findById that causes it to return null, throwing NoSuchElementException is obscuring the bug.

  In conclusion the first version is incorrect.

^{1 - I guess it is possible that the designer of the repository API has specified that Optional<FreePosts> findById(...) should return a null value instead of an Optional. But that would be a huge mistake, IMO.}

CodePudding user response：

To write the first version correctly, I need to null check from findById. Is my understanding correct?