TreeSet集合排序两种实现方式Comparable和Comparator比较

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

/**
 * TreeSet集合排序有两种方式，Comparable和Comparator区别：
 * 1：让元素自身具备比较性，需要元素对象实现Comparable接口，覆盖compareTo方法。
 * 2：让集合自身具备比较性，需要定义一个实现了Comparator接口的比较器，并覆盖compare方法，
 *   并将该类对象作为实际参数传递给TreeSet集合的构造函数。 第二种方式较为灵活。
 */
public class TreeSetDemo3 {
    public static void main(String[] args) {

        Teacher t1 = new Teacher(111L);
        Teacher t2 = new Teacher(222L);

        TreeSet teachers = new TreeSet();
        teachers.add(t1);
        teachers.add(t2);

        for (Iterator iter = teachers.iterator(); iter.hasNext();) {
            Teacher t =  iter.next();
            System.out.println(t.getId());
        }

        System.out.println("------------------------");

        Student s1 = new Student(123L);
        Student s2 = new Student(456L);                 //让集合自身具备比较性，这种方式较灵活
        TreeSet students = new TreeSet(new StudentComparator());

        students.add(s1);
        students.add(s2);

        for (Iterator iter = students.iterator(); iter.hasNext();) {
            Student s = iter.next();
            System.out.println(s.getId());
        }

    }
}

/**
 * 采用实现Comparable接口重写compareTo方法的方式，让元素自身具备比较性
 * @author Administrator
 *
 */
class Teacher implements Comparable{
    private Long id;

    public Teacher() {
    }
    public Teacher(Long id) {
        this.id = id;
    }

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }

    @Override
    public int compareTo(Teacher o) {
        return (int) (this.id - o.getId());
    }
}

//学生类
class Student {

    private Long id;

    public Student() {
    }
    public Student(Long id) {
        this.id = id;
    }

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
}

/**
 * 自定义定义一个实现了Comparator接口的比较器，并覆盖compare方法
 */
class StudentComparator implements Comparator {
    @Override
    public int compare(Student o1, Student o2) {
        return (int) (o1.getId() - o2.getId()); // 根据升序排序
    }
}