java-HashMap、TreeMap、LinkedHashMap、ArrayList、LinkedList使用笔记

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

    public static Map<String, Integer> sortEnemyMap(Map<String, Integer> unsortedMap){List<Map.Entry<String, Integer>> list = new LinkedList<>(unsortedMap.entrySet());// Sort the list based on valuesCollections.sort(list, new Comparator<Map.Entry<String, Integer>>() {public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {//由大到小return (o2.getValue()).compareTo(o1.getValue());//由小到大//return (o1.getValue()).compareTo(o2.getValue());}});// Convert list to map againMap<String, Integer> sortedMap = new LinkedHashMap<>();for (Map.Entry<String, Integer> entry : list) {sortedMap.put(entry.getKey(), entry.getValue());}return 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());