背景

Map<String, Integer> unsortedMap = new HashMap<>();  
unsortedMap.put("One", 1);  
unsortedMap.put("Two", 2);  
unsortedMap.put("Three", 3);  
unsortedMap.put("Four", 4);  

一、关于排序

1. TreeMap：默认按照key排序
2. 按照value排序，可使用如下代码

List<Map.Entry<String, Integer>> list = new LinkedList<>(unsortedMap.entrySet());  // Sort the list based on values  
Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {  public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {  return (o1.getValue()).compareTo(o2.getValue());  }  
});  // Convert list to map again  
Map<String, Integer> sortedMap = new LinkedHashMap<>();  
for (Map.Entry<String, Integer> entry : list) {  sortedMap.put(entry.getKey(), entry.getValue());  
}  
System.out.println("Sorted map by value: " + sortedMap);

二、关于转换

1. HashMap转TreeMap

Map<String, Integer> sortedMap = new TreeMap<>(unsortedMap);

2. HashMap转LinkedList

List<Map.Entry<String, Integer>> list = new LinkedList<>(unsortedMap.entrySet());