TreeSet中的排序问题——Comparable

package com.etc.hashset;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

public class TestHashSet {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		Set set=new TreeSet();
		set.add(new Student("zhangsan",20));
		set.add(new Student("zhangsan",20));
		set.add(new Student("zhangsan5",29));
		set.add(new Student("zhangsan3",25));
		set.add(new Student("zhangsan7",27));
		set.add(new Student("zhangsan1",21));

	    Iterator it = set.iterator();
	    int num=0;
	    while(it.hasNext()){
	    	System.out.println(num+++"-"+it.next());
	    }
	}
}
/**
 * Comparable是专门用来对TreeSet和TreeMap进行排序用的，comparable是自然排序，所以在对象所在的类实现该接口即可，TreeSet就不需要再指定专门的构造器
 *
 */
class Student implements Comparable {

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}

        //重写了该方法，用来判断是否是同一对象
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Student other = (Student) obj;
		if (age != other.age)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}

	public Student() {

	}

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

	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;
	}

	String name;
	int age;

	@Override
	public int compareTo(Object o) {
		if(o instanceof Student){
			Student stu=(Student)o;
			return this.age-stu.age;
		}
		return 0;
	}

	@Override
	public String toString() {
		return "Student [name=" + name + ", age=" + age + "]";
	}
}