java.lang.Comparable 接口的功用

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;
  }
}

TestComparable类：

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);
	}
}

打印结果：

ID:0  NAME:张零  SEX:0
ID:1  NAME:张一  SEX:0
ID:2  NAME:张二  SEX:0
ID:3  NAME:张三  SEX:0
ID:4  NAME:张四  SEX:1
ID:5  NAME:张五  SEX:0
ID:6  NAME:张六  SEX:1
ID:7  NAME:张七  SEX:1
ID:8  NAME:张八  SEX:1
ID:9  NAME:张九  SEX:0


其他无序集合也可以使用此接口，注意对于TreeMap是无效的哦！

感谢您的光临，有什么不对的地方还请高手指出！谢谢！