如何使用 Java stream 收集来创建 map，而不是 ZA8CFFDE6331BD59EB666AC9C

Question

I have the following...

public Map<Object, Integer> getRankings(){
    Stream<String> stream = votes.stream();
    Map<Object, Integer> map = stream
            .collect(Collectors.toMap(s -> s, s -> 1, Integer::sum));
    return Vote.sortByValues(map);
}

But I would like the return type to be Map<String, Integer> instead. How do I coerce the Object to a String ?

Answer 1

Since you have a Stream<String> , it can be inferred by just declaring the map with a key type of String :

Map<String, Integer> map =
    stream.collect(Collectors.toMap(s -> s, s -> 1, Integer::sum));

Answer 2

There's no problem in this:

public Map<String, Integer> getRankings(){
    Stream<String> stream = votes.stream();
    Map<String, Integer> map = stream
            .collect(Collectors.toMap(s -> s, s -> 1, Integer::sum));
    return Vote.sortByValues(map);
}