sort HashMap in reverse? [duplicate]

问题

This question already has answers here:

How to use a Java8 lambda to sort a stream in reverse order? (7 answers)

Comparator.reversed() does not compile using lambda (2 answers)

Closed 2 years ago.

So I came across this method which is able to sort HashMaps by value.

public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) {
        return map.entrySet()
                .stream()
                .sorted(Map.Entry.comparingByValue())
                .collect(Collectors.toMap(
                        Map.Entry::getKey,
                        Map.Entry::getValue,
                        (e1, e2) -> e1,
                        LinkedHashMap::new
                        ));
    }

I want to use the reversed() method on the Comparator but I can't seem to find the right place to put it.

回答1:

The reversed() method should be called on the Comparator returned by comparingByValue(). Java's type inference breaks down here, unfortunately, so you'll have to specify the generic types:

public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue
    (Map<K, V> map) {

    return map.entrySet()
            .stream()
            .sorted(Map.Entry.<K, V> comparingByValue().reversed())
            // Type here -----^ reversed() here -------^
            .collect(Collectors.toMap(
                    Map.Entry::getKey,
                    Map.Entry::getValue,
                    (e1, e2) -> e1,
                    LinkedHashMap::new
            ));
}

来源：https://stackoverflow.com/questions/42535050/sort-hashmap-in-reverse