Java8 - 在Map中搜索值

Question

I'm learning Java8 and looking to see how you could convert the following into Java8 streaming API where it 'stops' after finding the first 'hit' (like in the code below)

public int findId(String searchTerm) {

    for (Integer id : map.keySet()) {
        if (map.get(id).searchTerm.equalsIgnoreCase(searchTerm))
            return id;
    }
    return -1;
}

Answer 1

Without testing, something like this should work :

return map.entrySet()
          .stream()
          .filter(e-> e.getValue().searchTerm.equalsIgnoreCase(searchTerm))
          .findFirst() // process the Stream until the first match is found
          .map(Map.Entry::getKey) // return the key of the matching entry if found
          .orElse(-1); // return -1 if no match was found

This is a combination of searching for a match in the Stream of the entrySet and returning either the key if a match is found or -1 otherwise.

Answer 2

What you need is the Stream#findFirst() method once you have filtered the Stream using your predicate. Something like this:

map.entrySet()
    .stream()
    .filter(e -> e.getValue().equalsIgnoreCase(searchTerm))
    .findFirst();

This will return an Optional as there may not be any elements left after the filtering.