JAVA HashSet怎么使用(怎么才插入时不插入重复数据)?

import java.util.*;
public class HastSet
{
public static void main(String[] args)
{
HashSet hs=new HashSet();
hs.add(new Student(1,"zhangsan"));
hs.add(new Student(2,"lisi"));
hs.add(new Student(3,"wangwu"));
hs.add(new Student(1,"zhangsan"));
Iterator it=hs.iterator();
while(it.hasNext())
{
System.out.println(it.next());
}
}
}
class Student
{
int num;
String name;
Student(int num,String name)
{
this.num=num;
this.name=name;
}
public String toString()
{
return "num="+num+" "+"name="+name;
}
public int hashcode()
{
return num * name.hashCode();
}
public boolean equals(Student s)
{
return num==s.num && name.equals(s.name);
}

}

不可以插入相同的对象，像上面的Student，有2个具有相同的num和name，但是因为不是同一