基于java中的嵌套值对对象列表进行排序

Question

我有一个计划在多个日期交付的汽车列表，需要根据以下几点进行排序：

• 如果isReady>0,那么它应该首先显示在表中。然后该特定日期的其他值低于它。

• 如果isReady>0和对象gear!=null那么，它首先显示在该特定日期的表中。接下来是 Object 所在的其他值gear==null。

• 如果isReady>0、 Objectgear!=null和 Object tyre!=null，则该值将首先显示在该特定日期的表中。接下来是其他值，其中 Objectgear==null和tyre==null.

以下是class代码：

public class Car {

    private int isReady;

    private Tyre tyre;

    private Gear gear;

    private Date deliveryDate;

}

public class Gear {

    private int id;

    private String type;

}

public class Tyre {

    private int id;

    private String grip;

}

public class CarComparator implements Comparator<Car> {

    @Override

    public int compare(Car entry1, Car entry2) {

        int 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;

        }

        return value;

    }

}

我开发了一个比较器，它适用于第一个条件 where isReady>0。您能帮我解决上述其他条件吗？

提前致谢。

Answer 1

好吧，从 Java 8 开始，您可以像这样构建比较器：//order by delivery date first, ascending orderComparator<Car> carComparator = Comparator.comparing( Car::getDeliveryDate )&nbsp; //order by isReady in ascending order&nbsp; .thenComparing( Car::getIsReady )&nbsp; //we map null to 1 and non-null to -1 and ignore the rest for now&nbsp; .thenComparing( car -> car.getGear() != null ? -1 : 1 )&nbsp;&nbsp; .thenComparing( car -> car.getTyre() != null ? -1 : 1 );

Answer 2

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> {&nbsp; &nbsp; @Override&nbsp; &nbsp; public int compare(Car entry1, Car entry2) {&nbsp; &nbsp; &nbsp; &nbsp; int value;&nbsp; &nbsp; &nbsp; &nbsp; if (entry1.getDeliveryDate().before(entry2.getDeliveryDate())){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = -1;&nbsp; &nbsp; &nbsp; &nbsp; }else if (entry1.getDeliveryDate().equals(entry2.getDeliveryDate())){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = 0;&nbsp; &nbsp; &nbsp; &nbsp; }else{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value =1;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; //For same day&nbsp; &nbsp; &nbsp; &nbsp; if (value==0){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (entry1.getIsReady() > entry2.getIsReady()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else if (entry1.getIsReady() < entry2.getIsReady()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = 1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else if (entry1.getIsReady() == entry2.getIsReady()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; //if same isReady&nbsp; &nbsp; &nbsp; &nbsp; if (value==0){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (entry1.getGear()!=null && entry2.getGear()==null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else&nbsp; if (entry1.getGear()==null && entry2.getGear()==null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = 1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; //if still equals&nbsp; &nbsp; &nbsp; &nbsp; if (value==0){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (entry1.getTyre()!=null && entry2.getTyre()==null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = -1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else&nbsp; if (entry1.getTyre()==null && entry2.getTyre()==null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = 1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return value;&nbsp; &nbsp; }}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 {&nbsp; &nbsp; public static void main (String[]args) throws UnsupportedEncodingException, ParseException {&nbsp; &nbsp; &nbsp; &nbsp; List<Car> carL = new ArrayList<Car>();&nbsp; &nbsp; &nbsp; &nbsp; Car car1 = new Car();&nbsp; &nbsp; &nbsp; &nbsp; car1.setDeliveryDate(new Date());&nbsp; &nbsp; &nbsp; &nbsp; Gear gear1 = new Gear();&nbsp; &nbsp; &nbsp; &nbsp; car1.setGear(gear1);&nbsp; &nbsp; &nbsp; &nbsp; Tyre tyre1 = new Tyre();&nbsp; &nbsp; &nbsp; &nbsp; car1.setTyre(null);&nbsp; &nbsp; &nbsp; &nbsp; car1.setId(1);&nbsp; &nbsp; &nbsp; &nbsp; car1.setDeliveryDate((new SimpleDateFormat("dd-MM-yyyy")).parse("01-01-2000"));&nbsp; &nbsp; &nbsp; &nbsp; car1.setIsReady(0);&nbsp; &nbsp; &nbsp; &nbsp; Car car2 = new Car();&nbsp; &nbsp; &nbsp; &nbsp; car2.setDeliveryDate(new Date());&nbsp; &nbsp; &nbsp; &nbsp; Gear gear2 = new Gear();&nbsp; &nbsp; &nbsp; &nbsp; car2.setGear(gear2);&nbsp; &nbsp; &nbsp; &nbsp; Tyre tyre2 = new Tyre();&nbsp; &nbsp; &nbsp; &nbsp; car2.setTyre(tyre2);&nbsp; &nbsp; &nbsp; &nbsp; car2.setId(2);&nbsp; &nbsp; &nbsp; &nbsp; car2.setDeliveryDate((new SimpleDateFormat("dd-MM-yyyy")).parse("02-01-2000"));&nbsp; &nbsp; &nbsp; &nbsp; car2.setIsReady(1);&nbsp; &nbsp; &nbsp; &nbsp; Car car3 = new Car();&nbsp; &nbsp; &nbsp; &nbsp; car3.setDeliveryDate(new Date());&nbsp; &nbsp; &nbsp; &nbsp; Gear gear3 = new Gear();&nbsp; &nbsp; &nbsp; &nbsp; car3.setGear(gear3);&nbsp; &nbsp; &nbsp; &nbsp; Tyre tyre3 = new Tyre();&nbsp; &nbsp; &nbsp; &nbsp; car3.setTyre(tyre3);&nbsp; &nbsp; &nbsp; &nbsp; car3.setId(3);&nbsp; &nbsp; &nbsp; &nbsp; car3.setDeliveryDate((new SimpleDateFormat("dd-MM-yyyy")).parse("01-01-2000"));&nbsp; &nbsp; &nbsp; &nbsp; car3.setIsReady(1);&nbsp; &nbsp; &nbsp; &nbsp; carL.add(car1);&nbsp; &nbsp; &nbsp; &nbsp; carL.add(car2);&nbsp; &nbsp; &nbsp; &nbsp; carL.add(car3);&nbsp; &nbsp; &nbsp; &nbsp; Collections.sort(carL, new CarComparator());&nbsp; &nbsp; &nbsp; &nbsp; for (Car car : carL) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.println("car: " + car.toString());&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}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}

Answer 3

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> {&nbsp; &nbsp; @Override&nbsp; &nbsp; public int compare(Car entry1, Car entry2) {&nbsp; &nbsp; &nbsp; &nbsp; int value = 0;&nbsp; &nbsp; &nbsp; &nbsp; // might want to add a null check for either entry1 and entry2&nbsp; &nbsp; &nbsp; &nbsp; value = entry1.getDeliveryDate().compareTo(entry2.getDeliveryDate());&nbsp; &nbsp; &nbsp; &nbsp; if (value == 0) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = ((Integer)entry1.getIsReady()).compareTo((Integer)entry2.getIsReady());&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (value == 0) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = getIntegerValueForNullCheck(entry1.getGear()).compareTo(getIntegerValueForNullCheck(entry2.getGear()));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (value == 0) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = getIntegerValueForNullCheck(entry1.getTyre()).compareTo(getIntegerValueForNullCheck(entry2.getTyre()));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return value;&nbsp; &nbsp; }&nbsp; &nbsp; private Integer getIntegerValueForNullCheck (Object o) {&nbsp; &nbsp; &nbsp; &nbsp; return o == null ? 0 : 1;&nbsp; &nbsp; }}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 {&nbsp; &nbsp; public static void main(String[] args) {&nbsp; &nbsp; &nbsp; &nbsp; List<Car> cars = new LinkedList<>();&nbsp; &nbsp; &nbsp; &nbsp; Date today = new Date();&nbsp; &nbsp; &nbsp; &nbsp; Instant now = Instant.now();&nbsp; &nbsp; &nbsp; &nbsp; Instant after = now.plus(Duration.ofDays(1));&nbsp; &nbsp; &nbsp; &nbsp; Date tomorrow = Date.from(after);&nbsp; &nbsp; &nbsp; &nbsp; cars.add(new Car(5, new Tyre(1,"1"), new Gear(1, "1"), today ));&nbsp; &nbsp; &nbsp; &nbsp; cars.add(new Car(5, new Tyre(1,"1"), null, today ));&nbsp; &nbsp; &nbsp; &nbsp; cars.add(new Car(5, null, null, today ));&nbsp; &nbsp; &nbsp; &nbsp; cars.add(new Car(4, null, null, today ));&nbsp; &nbsp; &nbsp; &nbsp; cars.add(new Car(3, null, null, tomorrow ));&nbsp; &nbsp; &nbsp; &nbsp; Collections.sort(cars, new CarComparator());&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(cars);&nbsp; &nbsp; }}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}]

Answer 4

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> {&nbsp; &nbsp; @Override&nbsp; &nbsp; public int compare(Car entry1, Car entry2) {&nbsp; &nbsp; &nbsp; &nbsp; if (entry1.getisReady() > entry2.getisReady()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return -1;&nbsp; &nbsp; &nbsp; &nbsp; } else if (entry1.getisReady() < entry2.getisReady()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return 1;&nbsp; &nbsp; &nbsp; &nbsp; } else if (entry1.getisReady() == entry2.getisReady()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return 0;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}删除值和不同风格的比较：public class CarComparator implements Comparator<Car> {&nbsp; &nbsp; @Override&nbsp; &nbsp; public int compare(Car entry1, Car entry2) {&nbsp; &nbsp; &nbsp; &nbsp; if (entry1.getisReady() == entry2.getisReady()) return 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; return entry1.getisReady() > entry2.getisReady()? -1 : 1;&nbsp; &nbsp; }}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> {&nbsp; &nbsp; public int compare(Car entry1, Car entry2) {&nbsp; &nbsp; &nbsp; &nbsp; if (entry1.getisReady() == entry2.getisReady()) return 0;&nbsp; &nbsp; &nbsp; &nbsp; return entry1.getisReady() > entry2.getisReady()? -1 : 1;&nbsp; &nbsp; }&nbsp; &nbsp; public int compareGear(Car entry1, Car entry2){&nbsp; &nbsp; &nbsp; &nbsp; if ( (entry1.getGear() != null && entry2.getGear() != null)&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;||(entry1.getGear() == null && entry2.getGear() == null)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return compare(entry1, entry2);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; return entry1.getGear() != null && entry2.getGear() == null? -1 : 1;&nbsp; &nbsp; }&nbsp; &nbsp; public int compareTye(Car entry1, Car entry2){&nbsp; &nbsp; &nbsp; &nbsp; int order1 = entry1.getGear() != null && entry1.getTyre() != null? 1 : 0;&nbsp; &nbsp; &nbsp; &nbsp; int order2 = entry2.getGear() != null && entry2.getTyre() != null? 1 : 0;&nbsp; &nbsp; &nbsp; &nbsp; if ( order1 == order2 ) return compare(entry1, entry2);&nbsp; &nbsp; &nbsp; &nbsp; return order1 > order2? -1 : 1;&nbsp; &nbsp; }&nbsp;}