Java 如何使用Comparator定义自定义排序顺序?
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,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Java 如何使用Comparator定义自定义排序顺序?,java,sorting,enums,Java,Sorting,Enums,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,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; publ
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
}
}
class汽车实现可比性
{
私有字符串名称;
私有字符串颜色;
公共汽车(字符串名称、字符串颜色){
this.name=名称;
这个颜色=颜色;
}
//实现该类的自然顺序
公共内部比较(c车){
返回name.compareTo(c.name);
}
静态类ColorComparator实现Comparator{
公共int比较(车辆c1、车辆c2){
字符串a1=c1.5颜色;
字符串a2=c2.5颜色;
返回a1。比较(a2);
}
}
公共静态void main(字符串[]args){
List carList=new ArrayList();
List sortOrder=new ArrayList();
carList.add(新车(“福特”、“银色”);
添加(新车(“Tes”、“蓝色”));
添加(新车(“本田”、“洋红”);
排序器。添加(“银”);
添加(“洋红”);
排序器。添加(“蓝色”);
//现在我不知道如何实现自定义排序
}
}
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
}
及
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);
}
}
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());
}
}
}
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())));
}
};
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()));
Comparator carComparator=Comparator.comparating(
c->definedOrder.indexOf(c.getColor());
比较器在线路中
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());
}
});
List objList=findObj(名称);
Collections.sort(objList,newcomparator(){
@凌驾
公共整数比较(对象a1、对象a2){
返回a1.getType().compareToIgnoreCase(a2.getType());
}
});
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
}
公共类CarComparator实现Comparator{
//按此顺序将这些项目排序到列表的前面
私有静态列表顺序=Arrays.asList(“dd”、“aa”、“cc”、“bb”);
公共int比较(最终车辆o1,最终车辆o2){
int结果=0;
intO1Index=ORDER.indexOf(o1.getName());
intO2Index=ORDER.indexOf(o2.getName());
//如果在订单列表中找不到,则执行自然排序
//如果在订单列表中只找到一个,则将其浮动到另一个之上
//如果两者都在订单列表中,则进行索引比较
如果(o1Index<0&&o2Index<0)结果=o1.getName().compareTo(o2.getName());
如果(O1指数<0)结果=1,则为else;
如果(O2指数<0)结果=-1,则为else;
其他结果=O1指数-O2指数;
返回结果;
}
//测试输出:dd、aa、aa、cc、bb、bb、a、aaa、ac、ac、ba、bd、ca、cb、cb、cd、da、db、dc、zz
}
在Java 8中,您可以执行以下操作:
List<String> order = List.of("Red", "Green", "Magenta", "Silver");
Comparator.comparing(Car::getColor(), Comparator.comparingInt(c -> order.indexOf(c)))
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));
将一个枚举类型定义为
public enum Colors {
BLUE, SILVER, MAGENTA, RED
}
将color
的数据类型从String
更改为Colors
将color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());
}
}
我会这样做:
List<String> order = List.of("Red", "Green", "Magenta", "Silver");
Comparator.comparing(Car::getColor(), Comparator.comparingInt(c -> order.indexOf(c)))
List order=List.of(“红色”、“绿色”、“洋红”、“银色”);
Comparator.comparing(Car::getColor(),Comparator.comparingInt(c->order.indexOf(c)))
所有的积分都归@Sean Patrick Floyd:)使用简单的循环:
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){
}
}
}
}
publicstaticvoidcomparestorder(列表排序器、列表排序器){
int currentSortingLevel=0;
对于(int i=0;i如何运行此示例。在ColorComparator中无法访问PaintColors。您能否说明主要方法的外观。输出是什么?它始终是银色的吗?@Deepak:是的,enum
值的自然顺序是其值定义的顺序。@SeanPatrickFloyd我不认为依赖于枚举的自然排序是一种最佳做法。@mike我不同意,但这两种观点都有有效的参数。这不是自定义排序。此外,这不是一种“函数式”排序方式……这会产生副作用!!请您也研究一下这个问题。谢谢。Comparator carComparator=Comparator.comparating(c->definedOrder.indexOf(c.getColor());
正在编译errors@SantosshKumhar下面是一个工作示例:
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());
}
}
}
List<String> order = List.of("Red", "Green", "Magenta", "Silver");
Comparator.comparing(Car::getColor(), Comparator.comparingInt(c -> order.indexOf(c)))
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){
}
}
}
}
public static List<String> ALARMS_LIST = Arrays.asList(
"CRITICAL",
"MAJOR",
"MINOR",
"WARNING",
"GOOD",
"N/A");