1. java8 stream里排序相關(guān)方法

• Stream 里的sorted方法

Stream<T> sorted(Comparator<? super T> comparator);

• Comparator類

@FunctionalInterface
public interface Comparator<T> {
//定義自己的Comparator
 int compare(T o1, T o2);
...  
//使用comparing方法定義Comparator
public static <T, U extends Comparable<? super U>> Comparator<T> comparing（Function<? super T, ? extends U> keyExtractor){
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)
            (c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
    }
}
//使用comparingInt（按從小到大的順序）
public static <T> Comparator<T> comparingInt(ToIntFunction<? super T> keyExtractor) {
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)
            (c1, c2) -> Integer.compare(keyExtractor.applyAsInt(c1), keyExtractor.applyAsInt(c2));
    }

2. 實例

• 生成測試map

       Map<TopicNLPEnum, List<String>> map = new HashMap<>();
       map.put(TopicNLPEnum.SIMILAR, Arrays.asList("小說1", "言情1", "歷史1"));
       map.put(TopicNLPEnum.RELATIVE, Arrays.asList("小說3", "言情3", "歷史3"));
       map.put(TopicNLPEnum.ORIGIN, Arrays.asList("小說", "言情", "歷史"));
       map.put(TopicNLPEnum.TAGS, Arrays.asList("小說2", "言情2", "歷史2"));

• 使用comparing的方式new 一個Comparator

map.entrySet().stream()
       .sorted(Comparator.comparing(entry -> entry.getKey().getScore()))
       .forEach(entry -> System.out.println(entry.getValue()));

• 使用comparingInt

map.entrySet().stream()
       .sorted(Comparator.comparingInt(entry -> entry.getKey().getScore()))
       .forEach(entry -> System.out.println(entry.getValue()));

• 自定義Comparator

Comparator<Map.Entry<TopicNLPEnum, List<String>>> comp = (o1, o2) -> o1.getKey().getScore() - o2.getKey().getScore();
map.entrySet().stream()
       .sorted(comp)
       .forEach(entry -> System.out.println(entry.getValue()));

• 打印結(jié)果

[小說3, 言情3, 歷史3]
[小說2, 言情2, 歷史2]
[小說1, 言情1, 歷史1]
[小說, 言情, 歷史]