java - 如何在Java流中按值按降序对LinkedHashMap进行排序?

2022-01-22 00:00:00 sorting java-8 java java-stream linkedhashmap

要按升序排序，我可以使用:

To sort it int ascending order I can use:

myMap.entrySet().stream()
    .sorted(Map.Entry.comparingByValue())
    .collect(Collectors.toMap(Entry::getKey, Entry::getValue));

如何按降序进行?

推荐答案

要逆序排序，请将 Comparator.reverseOrder() 作为参数传递给 comparingByValue.

To sort in reverse order, pass Comparator.reverseOrder() as parameter to comparingByValue.

要获得 LinkedHashMap，您必须专门请求一个带有 4 参数的 toMap().如果你没有指定你想要什么样的映射，你会得到默认的，当前恰好是一个HashMap.由于 HashMap 不保留元素的顺序，它肯定不适合你.

To get a LinkedHashMap, you must specifically request one with the 4-argument toMap(). If you don't specify what kind of a map you want, you will get whatever the default is, which currently happens to be a HashMap. Since HashMap doesn't preserve the order of elements, it will definitely not do for you.

myMap.entrySet().stream()
        .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
        .collect(Collectors.toMap(
                Map.Entry::getKey, 
                Map.Entry::getValue, 
                (x,y)-> {throw new AssertionError();},
                LinkedHashMap::new
        ));

使用静态导入，它变得更令人愉快:

With static imports, it becomes a bit more pleasant:

myMap.entrySet().stream()
        .sorted(comparingByValue(reverseOrder()))
        .collect(toMap(
                Map.Entry::getKey, 
                Map.Entry::getValue, 
                (x,y)-> {throw new AssertionError();},
                LinkedHashMap::new
        ));

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