4 回答
TA贡献1900条经验 获得超5个赞
好吧,从 Java 8 开始,您可以像这样构建比较器:
//order by delivery date first, ascending order
Comparator<Car> carComparator = Comparator.comparing( Car::getDeliveryDate )
//order by isReady in ascending order
.thenComparing( Car::getIsReady )
//we map null to 1 and non-null to -1 and ignore the rest for now
.thenComparing( car -> car.getGear() != null ? -1 : 1 )
.thenComparing( car -> car.getTyre() != null ? -1 : 1 );
TA贡献1848条经验 获得超10个赞
检查此比较器,以便您可以使用多个属性进行排序
public class CarComparator implements Comparator<Car> {
@Override
public int compare(Car entry1, Car entry2) {
int value;
if (entry1.getDeliveryDate().before(entry2.getDeliveryDate())){
value = -1;
}else if (entry1.getDeliveryDate().equals(entry2.getDeliveryDate())){
value = 0;
}else{
value =1;
}
//For same day
if (value==0){
if (entry1.getIsReady() > entry2.getIsReady()) {
value = -1;
} else if (entry1.getIsReady() < entry2.getIsReady()) {
value = 1;
} else if (entry1.getIsReady() == entry2.getIsReady()) {
value = 0;
}
}
//if same isReady
if (value==0){
if (entry1.getGear()!=null && entry2.getGear()==null) {
value = -1;
} else if (entry1.getGear()==null && entry2.getGear()==null) {
value = 0;
} else{
value = 1;
}
}
//if still equals
if (value==0){
if (entry1.getTyre()!=null && entry2.getTyre()==null) {
value = -1;
} else if (entry1.getTyre()==null && entry2.getTyre()==null) {
value = 0;
} else{
value = 1;
}
}
return value;
}
}
我不确定这是否是您尝试做的。上面的比较器的作用是:首先对日期进行排序,如果找到相等的日期(值=0),则比较 isReady,然后比较 getGear(),最后比较 getTyre()。
这样您就可以在比较器中添加所需数量的属性。
包括3辆车的主要方法
public class Main {
public static void main (String[]args) throws UnsupportedEncodingException, ParseException {
List<Car> carL = new ArrayList<Car>();
Car car1 = new Car();
car1.setDeliveryDate(new Date());
Gear gear1 = new Gear();
car1.setGear(gear1);
Tyre tyre1 = new Tyre();
car1.setTyre(null);
car1.setId(1);
car1.setDeliveryDate((new SimpleDateFormat("dd-MM-yyyy")).parse("01-01-2000"));
car1.setIsReady(0);
Car car2 = new Car();
car2.setDeliveryDate(new Date());
Gear gear2 = new Gear();
car2.setGear(gear2);
Tyre tyre2 = new Tyre();
car2.setTyre(tyre2);
car2.setId(2);
car2.setDeliveryDate((new SimpleDateFormat("dd-MM-yyyy")).parse("02-01-2000"));
car2.setIsReady(1);
Car car3 = new Car();
car3.setDeliveryDate(new Date());
Gear gear3 = new Gear();
car3.setGear(gear3);
Tyre tyre3 = new Tyre();
car3.setTyre(tyre3);
car3.setId(3);
car3.setDeliveryDate((new SimpleDateFormat("dd-MM-yyyy")).parse("01-01-2000"));
car3.setIsReady(1);
carL.add(car1);
carL.add(car2);
carL.add(car3);
Collections.sort(carL, new CarComparator());
for (Car car : carL) {
System.out.println("car: " + car.toString());
}
}
}
输出:
car: Car{id=3, isReady=1, tyre=false, gear=false, deliveryDate=Sat Jan 01 00:00:00 EET 2000}
car: Car{id=1, isReady=0, tyre=true, gear=false, deliveryDate=Sat Jan 01 00:00:00 EET 2000}
car: Car{id=2, isReady=1, tyre=false, gear=false, deliveryDate=Sun Jan 02 00:00:00 EET 2000}
TA贡献1818条经验 获得超8个赞
为什么不重用 Integer.compareTo 来使代码更短?
像这样:
import java.util.Comparator;
public class CarComparator implements Comparator<Car> {
@Override
public int compare(Car entry1, Car entry2) {
int value = 0;
// might want to add a null check for either entry1 and entry2
value = entry1.getDeliveryDate().compareTo(entry2.getDeliveryDate());
if (value == 0) {
value = ((Integer)entry1.getIsReady()).compareTo((Integer)entry2.getIsReady());
if (value == 0) {
value = getIntegerValueForNullCheck(entry1.getGear()).compareTo(getIntegerValueForNullCheck(entry2.getGear()));
if (value == 0) {
value = getIntegerValueForNullCheck(entry1.getTyre()).compareTo(getIntegerValueForNullCheck(entry2.getTyre()));
}
}
}
return value;
}
private Integer getIntegerValueForNullCheck (Object o) {
return o == null ? 0 : 1;
}
}
包括测试排序的代码:
import java.time.Duration;
import java.time.Instant;
import java.time.LocalDateTime;
import java.util.*;
public class Sorting {
public static void main(String[] args) {
List<Car> cars = new LinkedList<>();
Date today = new Date();
Instant now = Instant.now();
Instant after = now.plus(Duration.ofDays(1));
Date tomorrow = Date.from(after);
cars.add(new Car(5, new Tyre(1,"1"), new Gear(1, "1"), today ));
cars.add(new Car(5, new Tyre(1,"1"), null, today ));
cars.add(new Car(5, null, null, today ));
cars.add(new Car(4, null, null, today ));
cars.add(new Car(3, null, null, tomorrow ));
Collections.sort(cars, new CarComparator());
System.out.println(cars);
}
}
输出:
[Car{isReady=4, tyre=null, gear=null, deliveryDate=Thu Oct 10 11:27:20 IDT 2019}
, Car{isReady=5, tyre=null, gear=null, deliveryDate=Thu Oct 10 11:27:20 IDT 2019}
, Car{isReady=5, tyre=Tyre{id=1, grip='1'}, gear=null, deliveryDate=Thu Oct 10 11:27:20 IDT 2019}
, Car{isReady=5, tyre=Tyre{id=1, grip='1'}, gear=Gear{id=1, type='1'}, deliveryDate=Thu Oct 10 11:27:20 IDT 2019}
, Car{isReady=3, tyre=null, gear=null, deliveryDate=Fri Oct 11 11:27:20 IDT 2019}
]
TA贡献1155条经验 获得超0个赞
老实说,我没有发现你的代码有什么问题。也就是说,如果您的意图是当条目 1 大于条目 2 时返回 -1(与范数相反的顺序)。如果没有更多的代码需要阅读,我认为如果您尝试比较为您的用例构建的值更大或更小,您的代码将会起作用。
但是,我认为您的返回方法效率较低。您不需要返回值。您可以只返回一个实际值。
为了进行比较,您可以先比较 ==,然后再评估其余的。但这可能很难阅读代码,所以我给你两个版本。
删除值版本:
public class CarComparator implements Comparator<Car> {
@Override
public int compare(Car entry1, Car entry2) {
if (entry1.getisReady() > entry2.getisReady()) {
return -1;
} else if (entry1.getisReady() < entry2.getisReady()) {
return 1;
} else if (entry1.getisReady() == entry2.getisReady()) {
return 0;
}
}
}
删除值和不同风格的比较:
public class CarComparator implements Comparator<Car> {
@Override
public int compare(Car entry1, Car entry2) {
if (entry1.getisReady() == entry2.getisReady()) return 0;
return entry1.getisReady() > entry2.getisReady()? -1 : 1;
}
}
我不确定我是否正确地理解了您的意思,但如果我没有理解,我希望这段代码可以帮助您。我将它们分为 3 个方法,希望您能获得 getTyre() 和 getGear() 方法。您可以根据需要组合它们,对于最后一个方法,其值被分成变量顺序以便于阅读代码。
class CarComparator implements Comparator<Car> {
public int compare(Car entry1, Car entry2) {
if (entry1.getisReady() == entry2.getisReady()) return 0;
return entry1.getisReady() > entry2.getisReady()? -1 : 1;
}
public int compareGear(Car entry1, Car entry2){
if ( (entry1.getGear() != null && entry2.getGear() != null)
||(entry1.getGear() == null && entry2.getGear() == null)
){
return compare(entry1, entry2);
}
return entry1.getGear() != null && entry2.getGear() == null? -1 : 1;
}
public int compareTye(Car entry1, Car entry2){
int order1 = entry1.getGear() != null && entry1.getTyre() != null? 1 : 0;
int order2 = entry2.getGear() != null && entry2.getTyre() != null? 1 : 0;
if ( order1 == order2 ) return compare(entry1, entry2);
return order1 > order2? -1 : 1;
}
}
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