Surprising results for HashSet

Question

Some thing wrong in my program? Please help me.
I am trying to create a TreeSet. I have created a class by name Person which implements equals(Object obj) method. In this program, I am trying to add an unique Person object (new Person(23,"test",6.3f,"blue")) twice to the HashSet. To my surprise takes. Again I am adding the same object to the 2nd HashSet. Then when I try to retainAll() method of the 1st HashSet and 2nd HashSet, I dont see any object being retained at all.
======================PROGRAM BELOW============================
==============================MAIN PRG=========================
import java.util.*;
public class TreeCompare
     public static void main(String args[])
          HashSet set1=new HashSet();
          HashSet set2=new HashSet();
          set1.add(new Person(20,"sun",5.5f,"blue"));
          set1.add(new Person(25,"moon",6.0f,"green"));
          set1.add(new Person(23,"test",6.3f,"blue"));
          set1.add(new Person(23,"test",6.3f,"blue"));
          System.out.println("\nFirst Set:\n"+set1);
          set2.add(new Person(23,"test",6.3f,"blue"));
          System.out.println("\nSecond Set:\n"+set2);
          set1.retainAll(set2);
          System.out.println("\nResultant Set:\n"+set1);
==============================PERSON CLASS=========================
class Person implements Comparable
     int      age;
     String      name;
     float      height;
     String      eye;
     public Person(int age,String name,float height,String eye)
          this.age=age;
          this.name=name;
          this.height=height;
          this.eye=eye;
     public boolean equals(Object obj)
          if(!(obj instanceof Person))
               return false;
          Person person=(Person) obj;
          return
                    (person.age==this.age)
                    &&(person.height==this.height)
                    &&(person.eye.equals(this.eye))
                    &&(person.name.equals(this.name))
     public String toString()
          return ("\n"+this.age+"\t"+this.name+"\t"+this.height+"\t"+this.eye+"\n");
     public int compareTo(Object obj)
          Person person=(Person) obj;
          if(this.age > person.age)
               return 1;
          }else if(this.age < person.age)
               return -1;
          }else if(this.height > person.height)
               return 1;
          }else if(this.height < person.height)
               return -1;
          }else
               int i=this.eye.compareTo(person.eye);
               if(i!=0)
                    return i;
               }else
                    int j=this.name.compareTo(person.name);
                    return j;
}

Answer 1

Something that is based on those four values, which always returns the same result when the four values are the same, and produces fairly random-looking results, like this:public int hashCode() {
  int value = age;
  value = 37 * value + name.hashCode();
  value = 37 * value + (int)height;
  value = 37 * value + eye.hashCode();
  return value;
}