Relationship between hashset and hashmap

 public class hashset 
  
    extends abstractset 
   
     implements set 
    
     , cloneable, Java. io. serializable {static final long serialversionuid =-5024744406713321676l; private transient hashmap 
     
       map; // dummy value to associate with an object in the backing map Private Static final object present = new object ();/*** constructs a new, empty set; the backing 
       hashmap  instance has * default initial capacity (16) and load factor (0.75 ). */Public hashset () {map = new hashmap 
      
        ();}......... /*** returns an iterator over the elements in this set. the elements * are returned in no special order. ** @ return an iterator over the elements in this set * @ see concurrentmodificationexception */Public iterator 
       
         iterator () {return map. keyset (). iterator () ;}
       
      
     
    
   
  

I seem to have met such an interviewer and asked about the relationship between the two. It turns out that hashset is used as hashmap, but value is omitted and key is used only.