Question

我有一个对象联系

public class Contact(){
   private Integer idContact
   private Date dateDebut;
    private Date dateFin;
    ...............
   public Contact(){}
  // getters and setters
}

和List<Contact>个联系人我想找到具有最小dateDebut的Object和使用Collections.sort(contacts)或其他方法的具有最大dateFin的Object。

Answer 1

创建内联匿名Comparator类并将其分配给常量：

public static final Comparator<Contact> DATE_DEBUT_COMPARATOR = new Comparator<Contact>() {
    public int compare(Contact c1, Contact c2) {
        return c1.dateDebut.compareTo(c2.dateDebut);
    }
}

Answer 2

您可以使用java.util.Collections.sort(List<T>, Comparator<? super T>)

Answer 3

static Comparator<Contact> DATEDEBUT_COMPARATOR = new Comparator<Contact>() {
    @Override
    public int compare(Contact first, Contact second) {
       assert(first != null);
       assert(second != null);
       return first.getDateDebut().compareTo(second.getDateDebut());
    }   
}

static Comparator<Contact> DATEFIN_COMPARATOR = new Comparator<Contact>() {
    @Override
    public int compare(Contact first, Contact second) {
       assert(first != null);
       assert(second != null);
       return first.getDateFin().compareTo(second.getDateFin());
    }   
}

Answer 4

static Comparator<Contact> DATE_DEBUT_COMPARATOR = new Comparator<Contact>() {
        @Override
        public int compare(Contact first, Contact second) {
           return first.getDateDebut().compareTo(second.getDateDebut());
        }  
        // Ascending order of debut date
    };


static Comparator<Contact> DATEFIN_COMPARATOR = new Comparator<Contact>() {
    @Override
    public int compare(Contact first, Contact second) {
      return second.getDateFin().compareTo(first.getDateFin());
    }   
    // Descending order of fin date
};

将comprator传递给Collections Util，可以在Arraylist的第一个位置找到最小首次亮相的对象

Collections.sort(contactList, DATE_DEBUT_COMPARATOR);

同样地将comprator传递给Collections Util，可以在Arraylist的第一个位置找到具有最大fin日期的对象

Collections.sort(contactList, DATE_FIN_COMPARATOR);

如何在一个对象中创建多个比较器

4 个答案: