java - 如何使用比较器接口(interface)按字符串键对映射进行排序

Question

我知道以前也有人问过类似的问题，但我有一个具体的问题，我不能弄错。

我想按一周中的几天对 map 进行排序，其中一周中的几天是 map 的键。如何在比较方法中比较没有自然顺序的字符串？排序末尾的 map 应该是:周一、周二、周三、周四。

这是到目前为止我的代码，但我陷入了比较方法。

    class OpeningTimes {

       private String openingTime;
       private String closingTime;
       public String getOpeningTime() {
           return openingTime;
       }
       public void setOpeningTime(String openingTime) {
           this.openingTime = openingTime;
       }
       public String getClosingTime() {
           return closingTime;
       }
       public void setClosingTime(String closingTime) {
           this.closingTime = closingTime;
       }

       @Override
       public String toString() {
           return new StringBuilder( "Opening Times: " + this.openingTime + " Closing Times: " + this.closingTime).toString();
       }
   }

比较器:

class OpeningTimesComparator implements Comparator<Map.Entry<String, OpeningTimes>>{

   @Override
   public int compare(Entry<String, OpeningTimes> o1, Entry<String, OpeningTimes> o2) {
       return 0; // what is the logic?
   }}

运行者:

public class TestClass {

    public static void main(String[] args) {

        Map<String, OpeningTimes> openingTimesMap = new TreeMap<String, OpeningTimes>();

        OpeningTimes openTime1 = new OpeningTimes();
        openTime1.setOpeningTime("9PM");
        openTime1.setClosingTime("10PM");

        OpeningTimes openTime2 = new OpeningTimes();
        openTime2.setOpeningTime("11PM");
        openTime2.setClosingTime("9PM");

        OpeningTimes openTime3 = new OpeningTimes();
        openTime3.setOpeningTime("13PM");
        openTime3.setClosingTime("14PM");

        OpeningTimes openTime4 = new OpeningTimes();
        openTime4.setOpeningTime("15PM");
        openTime4.setClosingTime("13PM");

        openingTimesMap.put("Tue", openTime2);
        openingTimesMap.put("Thu", openTime4);
        openingTimesMap.put("Mon", openTime1);
        openingTimesMap.put("Wed", openTime3);


        for (Entry<String, OpeningTimes> openingTimesSingle : openingTimesMap.entrySet()) {
            System.out.println("Key: " + openingTimesSingle.getKey() + " Value: " + openingTimesMap.get(openingTimesSingle.getKey()));
        }

        List<Map.Entry<String, OpeningTimes>> list = new ArrayList<Map.Entry<String, OpeningTimes>>(openingTimesMap.entrySet());

        Collections.sort(list, new OpeningTimesComparator());

        for (Entry<String, OpeningTimes> openingTimesSingle : openingTimesMap.entrySet()) {
            System.out.println("Key: " + openingTimesSingle.getKey() + " Value: " + openingTimesMap.get(openingTimesSingle.getKey()));
        }
    }
}

提前致谢

Answer 1

如果您必须使用包含自定义订单值的其他静态 map ，那么枚举将是一个很好的解决方案。

像这样定义一个枚举

enum Week{
  SUN,MON,TUE,WED,THU,FRI,SAT   
}

创建 EnumMap 的实例并添加条目，当您迭代 keySet 时，将按照枚举中提到的顺序检索条目

    Map<Week, String> map = new EnumMap<Week, String>(Week.class);

        map.put(Week.WED, "Wednesday");
        map.put(Week.SUN, "Sunday");
        map.put(Week.MON, "Monday");
        map.put(Week.THU, "Thursday");
        map.put(Week.SAT, "Saturday");
        map.put(Week.FRI, "Friday");
        map.put(Week.TUE, "Tuesday");


        for(Week week : map.keySet()){
            System.out.println(week + " -- " +map.get(week));
        }

输出:

SUN -- Sunday
MON -- Monday
TUE -- Tuesday
WED -- Wednesday
THU -- Thursday
FRI -- Friday
SAT -- Saturday

与我在枚举中定义的顺序相同。当然，仅当您的 Map 中的键范围有限(例如您的情况是一周中的几天)时，EnumMap 才有用且高效。希望这有帮助:)

选项 2:-

此方法的工作原理是假设 inputKeys 完全由您管理。请小心这一点，因为如果给定键不存在映射，它可能会给您带来 NPE。

private static Map<String,Integer> orderMappings = new HashMap<>();

    static{
        orderMappings.put("Sunday", 1);
        orderMappings.put("Monday", 2);
        orderMappings.put("Tuesday", 3);
        orderMappings.put("Wednesday", 4);
        orderMappings.put("Thursday", 5);
        orderMappings.put("Friday", 6);
        orderMappings.put("Saturday", 7);
    }

    class OrderComparator implements Comparator<String>{

        @Override
        public int compare(String key1, String key2) {
            int p1 = orderMappings.get(key1);
            int p2 =  orderMappings.get(key2);
            return p1-p2;
        }

    }