import java.util.*;
class HashSetTest
{
public static void main(String[] args)
{
HashSet hs=new HashSet();
/*hs.add("one");
hs.add("two");
hs.add("three");
hs.add("one");*/
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 int hashCode()
{
return num*name.hashCode();
}
public boolean equals(Object o)
{
Student s=(Student)o;
return num==s.num && name.equals(s.name);
}
public String toString()
{
return num+":"+name;
}
}
其中红色部分不知为什么要这样写,而不是return num=s.name.equals(s.name);
而且上面这段代码也在编译时出现错误.信息如下: