Qfyilyi

There is method, that have some condition flow and returning empty String ''(no space) in some case. Which method is more effective/faster to use in this case: String.isEmpty() or String.isBlack()?

String.isEmpty is marginally faster (~0.00219ms vs ~0.00206ms, about 6%). This is such a trivially small amount that there's no reason to worry about which one you use from a performance perspective.

Practically speaking, you should generally use String.isBlank if you expect potentially whitespace strings (e.g. from user input that may be all whitespace), and String.isEmpty when checking fields from the database, which will never contain a string of just whitespace.

String.isEmpty() will be better. Assuming that you are not expecting strings containing just whitespace returning a true value. If you want it to also treat strings containing whitespace as empty use String.isBlank()

The difference between the two is very slight but the docs specify what will be returned depending on input.

Faster here is very broad to classify, as you will need lot of considerations to test that out. It depends on what is your use case and accordingly which method fits in best.

String.isBlank handles any string even with white space, whereas the same is not true for String.isEmpty. So if you expect empty string ('') always, then using either of them should be fine.