java - 基于java中的嵌套值对对象列表进行排序

Question

I have a list of Cars scheduled for delivery for multiple dates which needs to be sorted on the basis of the below points:

• 如果isReady>0，那么它应该首先显示在表格中。和那么该特定日期的其他值就会低于它。
• 如果isReady>0并且对象gear!=null那么，它首先显示在该特定日期的表。后面跟着其他值，其中 Object gear==null。
• 如果 isReady>0、对象 gear!=null 和对象 tyre!=null，则该特定日期的值首先显示在表中。接下来是其他值，其中对象 gear==null 和 tyre==null。

以下是类代码:

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;
    }
}

I have developed a Comparator which works fine for the first condition where isReady>0. Could you please help me with the other conditions mentioned above.

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 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 );