java.lang.Comparable<T> 接口的作用
在开发中，我们可能会遇到需要将一些对象有序的放入到集合中，这时候我们只需要让类实现java.lang.Comparable<T>接口，并覆盖compareTo这个方法即可实现自动排序。下面给出例子，一个类Student类，一个测试类TestComparable，下面给出代码：
Studnet类：
public class Student implements Comparable{private int id;private String name;private int sex;public Student(int id, String name, int sex) { super(); this.id = id; this.name = name; this.sex = sex; }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 getSex() { return sex; }public void setSex(int sex) { this.sex = sex; }@Override public int compareTo(Object o) {int result = 0;//返回对比结果 0为相等，负整数为小于，正整数为大于if(o instanceof Student) {Student student = (Student)o;if(student.getId() > this.id) {return -1;} else if (student.getId() < this.id) {return 1;}} return result; }}import java.util.HashMap;public class TestComparable {private static HashMap<Integer, Student> studentMap;public static void main(String[] args) { loadStudent(); for(Student student : studentMap.values()) { System.out.println("ID:" + student.getId() + " NAME:" + student.getName() + " SEX:" + student.getSex()); } }private static void loadStudent() {studentMap = new HashMap<Integer, Student>();//请无视我对学生的命名吧。。。。毕竟用来测试的 呵呵Student student0 = new Student(2, "张二", 0);Student student1 = new Student(4, "张四", 1);Student student2 = new Student(6, "张六", 1);Student student3 = new Student(1, "张一", 0);Student student4 = new Student(3, "张三", 0);Student student5 = new Student(8, "张八", 1);Student student6 = new Student(9, "张九", 0);Student student7 = new Student(7, "张七", 1);Student student8 = new Student(0, "张零", 0);Student student9 = new Student(5, "张五", 0);studentMap.put(student0.getId(), student0);studentMap.put(student1.getId(), student1);studentMap.put(student2.getId(), student2);studentMap.put(student3.getId(), student3);studentMap.put(student4.getId(), student4);studentMap.put(student5.getId(), student5);studentMap.put(student6.getId(), student6);studentMap.put(student7.getId(), student7);studentMap.put(student8.getId(), student8);studentMap.put(student9.getId(), student9);studentMap.put(student0.getId(), student0);}}