Question

我想按降序对列表对象进行排序，并面对classCastException。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;

     class Student implements Comparator<Student>{
     private int id;
         private String name;

        public Student(int id, String name){
    this.id = id;
    this.name = name;
}

public int getId(){
    return id;
}
public String getName(){
    return name;
}

}

public class CollectionSearchDemo {


public static void main(String[] args) {

    List<Student> list = new ArrayList<Student>();
    list.add(new Student(3, "ouier"));
    list.add(new Student(2, "fdgds"));
    list.add(new Student(7, "kiluf"));
    list.add(new Student(1, "6trfd"));
    list.add(new Student(8, "hjgas"));
    list.add(new Student(5, "ewwew"));

    Collections.sort(list, new Comparator<Student>() {

        @Override
        public int compare(Student arg0, Student arg1) {

            return arg0.getId() - arg1.getId();
        }
    });

    Iterator iterator = list.iterator();
    while(iterator.hasNext()){
        Student student = (Student) iterator.next();
        System.out.print(student.getId()+":"+student.getName()+" ");
    }

    System.out.println("\nSorting in reverse order:");

//  Collections.reverse(list);
    Comparator<Student> collections = Collections.reverseOrder();
    Collections.sort(list, collections);     // here getting classCastException.

    Iterator iterator1 = list.iterator();
    while(iterator1.hasNext()){
        Student student = (Student) iterator1.next();
        System.out.print(student.getId()+":"+student.getName()+" ");
    }
}

}

想知道几句话。 1）什么是不同的赌注 Collection.reverse（名单）和 Comparator collections = Collections.reverseOrder（）; Collections.sort（列表，集合）; 2）为什么我面临classCastException。

Answer 1

您需要使用reverse()方法，

reverseOrder()

返回一个比较器，它对实现Comparable接口的对象集合施加自然顺序的反转。

所以ClassCastException

按降序排列对象列表

1 个答案: