如何使用comparator定义自定义排序顺序?

yqlxgs2m  于 2021-08-20  发布在  Java
关注(0)|答案(9)|浏览(270)

我想开发一个汽车清单排序演示。我使用数据表来显示汽车列表。现在我想按汽车颜色对列表进行排序。这里不是按字母顺序排序。我想使用我的自定义排序顺序,如红色汽车先来,然后是蓝色,等等。
为此,我尝试使用java ComparatorComparable 但它只允许按字母顺序排序。
那么,有谁能指导我如何实现要使用的技术,从而加快排序速度呢。

class Car implements Comparable<Car>
{
    private String name;
    private String color;

    public Car(String name, String color){
        this.name = name;
        this.color = color;
    }

    //Implement the natural order for this class
    public int compareTo(Car c) {
        return name.compareTo(c.name);
    }

    static class ColorComparator implements Comparator<Car> {
        public int compare(Car c1, Car c2) {
            String a1 = c1.color;
            String a2 = c2.color;
            return a1.compareTo(a2);
        }
    }

    public static void main(String[] args) {
        List<Car> carList = new ArrayList<>();
        List<String> sortOrder = new ArrayList<>();

        carList.add(new Car("Ford","Silver"));
        carList.add(new Car("Tes","Blue"));
        carList.add(new Car("Honda","Magenta"));

        sortOrder.add("Silver");
        sortOrder.add("Magenta");
        sortOrder.add("Blue");

        // Now here I am confuse how to implement my custom sort             
    }
}
0yg35tkg

0yg35tkg1#

我建议您为汽车颜色创建一个枚举,而不是使用字符串,枚举的自然顺序将是您声明常量的顺序。

public enum PaintColors {
    SILVER, BLUE, MAGENTA, RED
}

static class ColorComparator implements Comparator<CarSort>
 {
     public int compare(CarSort c1, CarSort c2)
     {
         return c1.getColor().compareTo(c2.getColor());
     }
 }

将字符串更改为paintcolor,然后在主目录中,您的汽车列表变为:

carList.add(new CarSort("Ford Figo",PaintColor.SILVER));

...

Collections.sort(carList, new ColorComparator());
eoigrqb6

eoigrqb62#

这个怎么样:

List<String> definedOrder = // define your custom order
    Arrays.asList("Red", "Green", "Magenta", "Silver");

Comparator<Car> comparator = new Comparator<Car>(){

    @Override
    public int compare(final Car o1, final Car o2){
        // let your comparator look up your car's color in the custom order
        return Integer.valueOf(
            definedOrder.indexOf(o1.getColor()))
            .compareTo(
                Integer.valueOf(
                    definedOrder.indexOf(o2.getColor())));
    }
};

原则上,我同意使用 enum 是一种更好的方法,但此版本更灵活,因为它允许您定义不同的排序顺序。
更新
Guava将这一功能烘焙到它的 Ordering 类别:

List<String> colorOrder = ImmutableList.of("red","green","blue","yellow");
final Ordering<String> colorOrdering = Ordering.explicit(colorOrder);
Comparator<Car> comp = new Comparator<Car>() {
    @Override
    public int compare(Car o1, Car o2) {
        return colorOrdering.compare(o1.getColor(),o2.getColor());
    }
};

这个版本没有那么冗长。
再次更新
java 8使比较器更加简洁:

Comparator<Car> carComparator = Comparator.comparing(
        c -> definedOrder.indexOf(c.getColor()));
daupos2t

daupos2t3#

比较器在线。。。

List<Object> objList = findObj(name);
Collections.sort(objList, new Comparator<Object>() {
    @Override
    public int compare(Object a1, Object a2) {
        return a1.getType().compareToIgnoreCase(a2.getType());
    }
});
fivyi3re

fivyi3re4#

我认为可以这样做:

class ColorComparator implements Comparator<CarSort>
{
    private List<String> sortOrder;
    public ColorComparator (List<String> sortOrder){
        this.sortOrder = sortOrder;
    }

    public int compare(CarSort c1, CarSort c2)
    {
        String a1 = c1.getColor();
        String a2 = c2.getColor();
        return sortOrder.indexOf(a1) - sortOrder.indexOf(a2);
     }
 }

要进行排序,请使用以下命令:

Collections.sort(carList, new ColorComparator(sortOrder));
8cdiaqws

8cdiaqws5#

我不得不做一些类似肖恩和伊莱克斯的回答。
但是我有太多的选项来明确定义排序顺序,只需要将某些条目浮动到列表的前面。。。以指定的(非自然)顺序。
希望这对其他人有帮助。

public class CarComparator implements Comparator<Car> {

    //sort these items in this order to the front of the list 
    private static List<String> ORDER = Arrays.asList("dd", "aa", "cc", "bb");

    public int compare(final Car o1, final Car o2) {
        int result = 0;
        int o1Index = ORDER.indexOf(o1.getName());
        int o2Index = ORDER.indexOf(o2.getName());
        //if neither are found in the order list, then do natural sort
        //if only one is found in the order list, float it above the other
        //if both are found in the order list, then do the index compare
        if (o1Index < 0 && o2Index < 0) result = o1.getName().compareTo(o2.getName());
        else if (o1Index < 0) result = 1;
        else if (o2Index < 0) result = -1;
        else result = o1Index - o2Index;
        return result;
    }

//Testing output: dd,aa,aa,cc,bb,bb,bb,a,aaa,ac,ac,ba,bd,ca,cb,cb,cd,da,db,dc,zz
}
vxqlmq5t

vxqlmq5t6#

我会这样做:

List<String> order = List.of("Red", "Green", "Magenta", "Silver");

Comparator.comparing(Car::getColor(), Comparator.comparingInt(c -> order.indexOf(c)))

所有学分归@sean patrick floyd:)

moiiocjp

moiiocjp7#

在java 8中,您可以执行以下操作:
您首先需要一个枚举:

public enum Color {
    BLUE, YELLOW, RED
}

车辆等级:

public class Car {

    Color color;

    ....

    public Color getColor() {
        return color;
    }

    public void setColor(Color color) {
        this.color = color;
    }
}

然后,使用您的汽车列表,您可以简单地执行以下操作:

Collections.sort(carList, Comparator:comparing(CarSort::getColor));
ej83mcc0

ej83mcc08#

将一个枚举类型定义为

public enum Colors {
     BLUE, SILVER, MAGENTA, RED
}

更改的数据类型 color 从…起 StringColors 将颜色的getter和setter方法的返回类型和参数类型更改为 Colors 定义比较器类型如下

static class ColorComparator implements Comparator<CarSort>
{
    public int compare(CarSort c1, CarSort c2)
    {
        return c1.getColor().compareTo(c2.getColor());
    }
}

将元素添加到列表后,通过将列表和比较器对象作为参数传递来调用集合的排序方法
即, Collections.sort(carList, new ColorComparator()); 然后使用 ListIterator .
完整的类实现如下所示:

package test;

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

public class CarSort implements Comparable<CarSort>{

    String name;
    Colors color;

    public CarSort(String name, Colors color){
        this.name = name;
        this.color = color;
    } 

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Colors getColor() {
        return color;
    }
    public void setColor(Colors color) {
        this.color = color;
    }

    //Implement the natural order for this class
    public int compareTo(CarSort c)
    {
        return getName().compareTo(c.getName());
    }

    static class ColorComparator implements Comparator<CarSort>
    {
        public int compare(CarSort c1, CarSort c2)
        {
            return c1.getColor().compareTo(c2.getColor());
        }
    }

    public enum Colors {
         BLUE, SILVER, MAGENTA, RED
    }

     public static void main(String[] args)
     {
         List<CarSort> carList = new ArrayList<CarSort>();
         List<String> sortOrder = new ArrayList<String>();

         carList.add(new CarSort("Ford Figo",Colors.SILVER));
         carList.add(new CarSort("Santro",Colors.BLUE));
         carList.add(new CarSort("Honda Jazz",Colors.MAGENTA));
         carList.add(new CarSort("Indigo V2",Colors.RED));
         Collections.sort(carList, new ColorComparator());

         ListIterator<CarSort> itr=carList.listIterator();
         while (itr.hasNext()) {
            CarSort carSort = (CarSort) itr.next();
            System.out.println("Car colors: "+carSort.getColor());
        }
     }
}
u7up0aaq

u7up0aaq9#

仅使用简单循环:

public static void compareSortOrder (List<String> sortOrder, List<String> listToCompare){
        int currentSortingLevel = 0;
        for (int i=0; i<listToCompare.size(); i++){
            System.out.println("Item from list: " + listToCompare.get(i));
            System.out.println("Sorting level: " + sortOrder.get(currentSortingLevel));
            if (listToCompare.get(i).equals(sortOrder.get(currentSortingLevel))){

            } else {
                try{
                    while (!listToCompare.get(i).equals(sortOrder.get(currentSortingLevel)))
                        currentSortingLevel++;
                    System.out.println("Changing sorting level to next value: " + sortOrder.get(currentSortingLevel));
                } catch (ArrayIndexOutOfBoundsException e){

                }

            }
        }
    }

并按列表中的顺序排序

public static List<String> ALARMS_LIST = Arrays.asList(
            "CRITICAL",
            "MAJOR",
            "MINOR",
            "WARNING",
            "GOOD",
            "N/A");

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