java - 遍历Hash Map key的值是按降序还是升序？

Question

我试图以降序或升序遍历 HashMap ，但没有得到正确的输出。

这是我的 map :

Hashmap<String Integer> hm= new Hashmap<String,Integer>();

这是我的值(value)观:

Key    Value
Hi     4
kumar  1
Hello  1
vivek  3

我正在尝试这样的事情:

List<Integer> ValueList = new ArrayList<Integer>(hm.values());
                ArrayList<String> keyList = new ArrayList<String>(hm.keySet());

Collections.sort(ValueList);
                Collections.reverse(keyList);
                Collections.reverse(ValueList);

我想要这样的东西:

Key    Value
kumar  1
Hello  1
vivek  3
Hi     4

Answer 1

我建议使用Apache Commons Collections ListOrderedMap。解决办法如下:

//Populate the map
Map<String, Integer> map = new HashMap<>();
map.put("Hi", 4);
map.put("kumar", 1);
map.put("Hello", 1);
map.put("vivek", 3);

//Sort the values
List<Integer> values = new ArrayList<Integer>(map.values());
Collections.sort(values);

int size = values.size();
Set<Entry<String, Integer>> entries = map.entrySet();

//Create a new ordered map
ListOrderedMap<String, Integer> orderedMap;
orderedMap = ListOrderedMap.listOrderedMap(new HashMap<String, Integer>(map));

for (int i = 0; i < size; i++) {

    Integer value = values.get(i);
    Iterator<Entry<String, Integer>> iter = entries.iterator();

    while (iter.hasNext()) {
        Entry<String, Integer> entry = iter.next();
        if (value.equals(entry.getValue())) {
            //Put all values at index i that match the value
            orderedMap.put(i, entry.getKey(), value);
        }
    }
}

//Print the orderedMap key/value pairs
entries = orderedMap.entrySet();
for (Entry<String, Integer> entry : entries) {
    final String key = entry.getKey();
    final Integer value = entry.getValue();
    System.out.println("key = " + key + ", value = " + value);
}

输出:

key = Hello, value = 1
key = kumar, value = 1
key = vivek, value = 3
key = Hi, value = 4