如何根据这些条件对对象的 HashSet 进行排序？

Question

我在这里整理了一个 SSCCE：

House.java：

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class House {

    private Status currentStatus;
    private String city;
    private Date date;

    public enum Status { AVAILABLE, 
                         SOLD, 
                         CONTINGENT 
    }

    public House(Status s, String c, String d) throws ParseException {
        currentStatus = s;
        city = c;
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        date = sdf.parse(d);
    }
}

SortingTest.java：

import java.text.ParseException;
import java.util.HashSet;
import sortingtest.House.Status;    

public class SortingTest {


    public static void main(String[] args) throws ParseException {
        HashSet<House> houses = new HashSet<House>();
        houses.add(new House(Status.AVAILABLE, "New York City", "2007-11-11"));
        houses.add(new House(Status.SOLD, "Los Angeles", "2005-06-11"));
        houses.add(new House(Status.AVAILABLE, "Chicago", "2012-05-03"));
        houses.add(new House(Status.CONTINGENT, "Portland", "2007-10-11"));

        //Sort HashSet of House objects by criteria listed below      

        //sort by Status.AVAILABLE
            //call sort
            //System.out.println("Sorted by available");
            //iterate set and print out sorted houses

        //sort by Status.SOLD
            //call sort
            //System.out.println("Sorted by sold");
            //iterate set and print out sorted houses

        //sort by Status.CONTINGENT
            //call sort
            //System.out.println("Sorted by contingent");
            //iterate set and print out sorted houses

        //sort by City
            //call sort
            //System.out.println("Sorted alphabetically by City");
            //iterate set and print out sorted houses

        //sort by City
            //call sort
            //System.out.println("Sorted reverse alphabetically by City");
            //iterate set and print out sorted houses

        //sort by Date (newest)
            //call sort
            //System.out.println("Sorted by newest date (fewest days on market)");
            //iterate set and print out sorted houses

        //sort by Date (oldest)
            //call sort
            //System.out.println("Sorted oldest date (most days on market)");
            //iterate set and print out sorted houses
    }
}

所以最终我想创建一个SetSorter 类，我可以在其中调用一个方法，该方法将返回以特定格式排序的 Set。

如果您不想阅读代码中的 cmets，我想根据以下条件进行排序：

• 状态.可用
• 状态.已售出
• 状态.条件
• 城市（按字母顺序）
• 城市（字母倒序）
• 日期（上市最短天数）
• 日期（上市时间最多）

我对它进行了一些阅读，看起来人们建议将其制成 TreeSet 以进行排序和使用比较器。我见过很多例子，人们要么为比较器创建一个单独的类，要么使指定的类实现可比较。

我还没有看到有人编写了一个额外的类来处理所有的排序。这可能吗？如果是这样，有人可以告诉我从哪里开始吗？这些比较似乎比典型的整数比较稍微复杂一些。

编辑澄清

当按 Status.AVAILABLE 排序时，我希望 Set 让对象按以下方式显示：

• Status.AVAILABLE（在顶部/第一）
• Status.CONTINGENT（在 Status.AVAILABLE/秒之后）
• Status.SOLD（在 Status.CONTINGENT/last 之后）

当按 Status.CONTINGENT 排序时，我希望按如下方式排序：

• 状态.CONTINGENT
• 状态.已售出
• 状态.可用

当按 Status.SOLD 排序时，我希望集合按如下方式排序：

• 状态.已售出
• 状态.CONTINGENT
• 状态.可用

编辑 #2 终极目标：

我想要一个类，我可以简单地调用方法来对集合进行排序。

即：

//sort by date
SetSorter.sortByData(treeSet);    //returns TreeSet sorted by date

//sort by city
SetSorter.sortByCity(treeSet);    //returns TreeSet sorted by City

//sort by other criteria 

编辑#3

class SortByCity implements Comparator<House> {
    @Override
    public int compare(House h1, House h2) {
        return h1.getCity().compareTo(h1.getCity());
    } 
}


houses = new TreeSet(new SortByCity());

我认为这是一种简单的方法，但这些都是小类，而且（在我看来）看起来很乱。谁想在 .java 中包含 7 个迷你类？

谁能提供一些替代的例子让我看看？

Answer 1

这里有一些关于排序的示例。我没有执行日期或反向字母排序（这是一项任务）。请注意关于比较两所房子的价值0的内联评论！

public class HouseSorter {

    enum Status {
        SOLD, AVAILABLE, CONTINGENT;
    }

    /**
     * Immutable house (if a house is sold or not does not change a house, use a
     * Map instead).
     */
    private static class House {
        private final String city;

        House(String city) {
            this.city = city;
        }

        public String getCity() {
            return city;
        }

        @Override
        public String toString() {
            return "House in " + city;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == null) {
                return false;
            }
            if (!House.class.isAssignableFrom(obj.getClass())) {
                return false;
            }
            return this.city.equalsIgnoreCase(((House) obj).city);
        }

        @Override
        public int hashCode() {
            return city.hashCode();
        }
    }

    public static SortedSet<House> sortAlphabetically(Set<House> houses) {
        TreeSet<House> sortedHouses = new TreeSet<House>(
                new Comparator<House>() {
                    @Override
                    public int compare(House o1, House o2) {
                        return o1.getCity().compareTo(o2.getCity());
                    }
                });
        sortedHouses.addAll(houses);
        return sortedHouses;
    }

    public static SortedSet<House> sortByStatus(
            final Map<House, Status> houseStatusMap) {
        TreeSet<House> sortedHouses = new TreeSet<House>(
                new Comparator<House>() {
                    @Override
                    public int compare(House o1, House o2) {
                        int compareByStatus = houseStatusMap.get(o1).compareTo(
                                houseStatusMap.get(o2));
                        if (compareByStatus != 0) {
                            return compareByStatus;
                        }
                        // you need an additional compare, until none of the
                        // houses compare with result 0
                        // otherwise the houses would be equal and therefore
                        // removed from the set
                        return o1.getCity().compareTo(o2.getCity());
                    }
                });
        sortedHouses.addAll(houseStatusMap.keySet());
        return sortedHouses;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        final Map<House, Status> houseStatusMap = new HashMap<House, Status>();
        House house0 = new House("Beverwijk");
        houseStatusMap.put(house0, Status.SOLD);
        House house1 = new House("Opmeer");
        houseStatusMap.put(house1, Status.SOLD);
        House house2 = new House("Amstelveen");
        houseStatusMap.put(house2, Status.AVAILABLE);
        House house3 = new House("Haarlem");
        houseStatusMap.put(house3, Status.CONTINGENT);

        System.out.println(sortAlphabetically(houseStatusMap.keySet()));
        System.out.println(sortByStatus(houseStatusMap));
    }
}