Bagaimanakah kita boleh melaksanakan HashSet tersuai dalam Java?

public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, Serializable

import java.util.*;
public class CustomHashSetTest extends AbstractSet<object> {
   private HashMap<Object, Object> map = null;
   private static final Object tempObject = new Object();
   public CustomHashSetTest() {
      map = new HashMap<>();
   }
   public boolean add(Object object) {
      return map.put(object, tempObject)==null;
   }
   public static void main(String[] args) {
      CustomHashSetTest test = new CustomHashSetTest();
      test.add("India");
      test.add("Australia");
      test.add("England");
      test.add("Australia");
      for(Object object : test) {
         System.out.println(object.toString());
      }
   }
   @Override
   public Iterator<object> iterator() {
      return map.keySet().iterator();
   }
   @Override
   public int size() {
      return map.size();
   }
}
</object></object>