Java提供内置实用程序方法*sort（）和Comparator集合。reverseOrder（）*按降序对对象排序。

在Java中按降序对用户定义的对象排序

Collections.sort(persons, Collections.reverseOrder());

这个示例演示了我们创建一个person对象列表，并使用Comparable接口的*compateTo（）*方法比较每个人的年龄。简而言之，我们正在按年龄降序对人进行分类。
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public class Person implements Comparable < Person > {
    private int id;
    private String name;
    private int age;
    public Person(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return this.name;
    }
    @Override
    public int compareTo(Person otherPerson) {
        return (this.getAge() - otherPerson.getAge());
    }
}

注意，Person类实现Comparable接口并提供compareTo()方法实现。
下面是测试和排序person对象的代码：

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class PersonSorterInASC {
    public static void main(String[] args) {
        sortUserDefinedObjectsInAsc();
    }
    private static void sortUserDefinedObjectsInAsc() {
        List < Person > persons = new ArrayList < Person > ();
        Person person1 = new Person(59, "John", 40);
        Person person12 = new Person(67, "Roger", 25);
        Person person13 = new Person(45, "Steven", 30);
        persons.add(person1);
        persons.add(person12);
        persons.add(person13);
        System.out.println("Before Sorting : " + persons);
        Collections.sort(persons, Collections.reverseOrder());
        System.out.println("After Sorting : " + persons);
    }
}

输出：

Before Sorting : [John, Roger, Steven]
Sort in decending order : [John, Steven, Roger]