如何为用户定义的类实现通用比较器

Question

我想对包含一些数据成员的用户定义类进行排序。 在这里，我创建了名为 Universal & Showroom 的类，它们都包含 common 的价格标签。我想创建通用的 Comparator compare()，这对于两个类来说都是通用的，两个类都具有具有不同值的相同字段。 两个值都按升序排序。

public class Showroom  {
    String phone_vendor;int price,ram,storage;

    public Showroom(String phone_vendor, int price, int ram, int storage) {
        this.phone_vendor = phone_vendor;
        this.price = price;
        this.ram = ram;
        this.storage = storage;
    }

}
public class Universal {
    String phone_vendor;
    int price,ram,storage;

    public Universal(String phone_vendor, int price, int ram,int storage) {
        this.phone_vendor = phone_vendor;
        this.price = price;
        this.ram = ram;
        this.storage=storage;
    }
}

Answer 1

只是我之前给出的评论示例。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public abstract class Parent {
    String phone_vendor;int price,ram,storage;

    public Parent(String phone_vendor, int price, int ram, int storage) {
        this.phone_vendor = phone_vendor;
        this.price = price;
        this.ram = ram;
        this.storage = storage;
    }

    public static void main(String[] args) {
        Universal us = new Universal("Samsung", 51, 5, 11);
        Showroom sr = new Showroom("Nokia", 50, 4, 10);

        List<Parent> lst = new ArrayList<Parent>();
        lst.add(us);
        lst.add(sr);
        Collections.sort(lst, new PriceComparator());

        for(Parent p:lst) {
            System.out.println(p.price);
        }

    }
}


class Showroom extends Parent {

    public Showroom(String phone_vendor, int price, int ram, int storage) {
        super(phone_vendor, price, ram, storage);
    }

}
class Universal extends Parent {
   public Universal(String phone_vendor, int price, int ram, int storage) {
       super(phone_vendor, price, ram, storage);
   }
}

class PriceComparator implements Comparator<Parent> {
    @Override
    public int compare(Parent o1, Parent o2) {
        return o1.price - o2.price;
    }
}

Answer 2

泛型的另一种选择：

    import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class GenericComparator<T> implements Comparator<T> {

    @Override
    public int compare(T o1, T o2) {
        int price1 = 0;
        int price2 = 0;
        try {
            Method m1 = o1.getClass().getDeclaredMethod("getPrice", o1.getClass().getClasses());
            price1 = (int) m1.invoke(o1);
            Method m2 = o2.getClass().getDeclaredMethod("getPrice", o1.getClass().getClasses());
            price2 = (int) m2.invoke(o2);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (SecurityException e) {
            e.printStackTrace();
        }
        return price1 - price2;
    }

    public static void main(String[] args) {
        List<Showroom> showRoomList = new ArrayList<Showroom>();
        showRoomList.add(new Showroom("IPHONE", 9000, 4, 4));
        showRoomList.add(new Showroom("SAMSUNG", 5000, 4, 4));
        showRoomList.add(new Showroom("MOTO", 8000, 4, 4));
        showRoomList.add(new Showroom("SONY", 7000, 4, 4));

        List<Universal> universalList = new ArrayList<Universal>();
        universalList.add(new Universal("IPHONE", 100000, 4, 4));
        universalList.add(new Universal("SAMSUNG", 222222, 4, 4));
        universalList.add(new Universal("MOTO", 44444, 4, 4));
        universalList.add(new Universal("SONY", 7055500, 4, 4));
        System.out.println("Showroom");
        Collections.sort(showRoomList, new GenericComparator<Showroom>());
        for (Showroom s : showRoomList) {
            System.out.println(s.getPrice());
        }
        System.out.println("Universal");
        Collections.sort(universalList, new GenericComparator<Universal>());
        for (Universal s : universalList) {
            System.out.println(s.getPrice());
        }
    }

}

输出：

Showroom
5000
7000
8000
9000
Universal
44444
100000
222222
7055500

注意：确保为 Universal 和 Showroom Pojos 中的属性创建 setter/getter。

Answer 3

有几种方法可以解决这个问题。

一种方法是定义一个接口，该接口可以访问您需要的信息，并为此接口实现比较器，以便可以比较实现它的每个类。

interface Offer {

    String phoneVendor();

    int price();

    int ram();

    int storage();

}

class OfferComparator implements Comparator<Offering> {

    @Override
    public int compare(Offering o1, Offering o2) {
        // Compare
        return 0;
    }

}

第二个选项是......如果它们看起来相同，你真的需要这两个类吗？您能否通过赋予它类型属性来概括它？合并的类可以实现可比较的。像这样的：

public class Offer implements Comparable<Offer> {

    enum Type {
        Showroom, Universal;
    }

    Type type;
    String phone_vendor;
    int price, ram, storage;

    public Showroom(String phone_vendor, int price, int ram, int storage) {
        this.phone_vendor = phone_vendor;
        this.price = price;
        this.ram = ram;
        this.storage = storage;
    }

    @Override
    public int compareTo(Offer o) {
        // Compare
        return 0;
    }

}