java中map的排序问题

java中Map排序问题

按key排序

public class MapSortDemo { public static void main(String[] args) { Map<String, String> map = new TreeMap<String, String>(); map.put("KFC", "kfc"); map.put("WNBA", "wnba"); map.put("NBA", "nba"); map.put("CBA", "cba"); Map<String, String> resultMap = sortMapByKey(map); for (Map.Entry<String, String> entry : resultMap.entrySet()) { System.out.println(entry.getKey() + " " + entry.getValue()); } } public static Map<String, String> sortMapByKey(Map<String, String> map) { if (map == null || map.isEmpty()) { return null; } Map<String, String> sortMap = new TreeMap<String, String>( new MapKeyComparator()); sortMap.putAll(map); return sortMap; } } class MapKeyComparator implements Comparator<String>{ @Override public int compare(String str1, String str2) { return str1.compareTo(str2); } }

按value排序

public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); while(sc.hasNext()){ Map<Character, Integer> map = new LinkedHashMap<>(); String sentence = sc.nextLine(); char[] arr = sentence.toCharArray(); for(int i=0;i<arr.length;i++){ if((arr[i] >= 'A' && arr[i] <= 'Z') || (arr[i] >='a' && arr[i] <= 'z')|| arr[i] >= '1' && arr[i] <= '9' || arr[i]==' '){ if(map.get(arr[i]) != null){ map.put(arr[i], map.get(arr[i])+1); }else{ map.put(arr[i], 1); } } } // 转化为list List<Map.Entry<Character, Integer>> entryList = new ArrayList<Map.Entry<Character, Integer>>( map.entrySet()); // public static <T> void sort(List<T> list, Comparator<? super T> c) Collections.sort(entryList, new MapValueComparator()); for (Map.Entry<Character, Integer> cc : entryList) { System.out.print(cc.getKey()); } } } private static class MapValueComparator implements Comparator<Map.Entry<Character, Integer>>{ @Override public int compare(Map.Entry<Character, Integer> o1, Map.Entry<Character, Integer> o2) { if(o1.getValue() < o2.getValue()) return 1; else if(o1.getValue() == o2.getValue()) return o1.getKey()-(o2.getKey()); else return -1; } } }