class User { 
   
   private String name; 
   
   User(String name) { 
      this.name = name; 
   } 
   @Override 
   public boolean equals(Object obj) { 
     if (!(obj instanceof User)) return false; 
  
     User other = (User) obj; 
     return name.equals(other.name); 
   } 
} 
Set users = new HashSet<>(); 
users.add(new User("Alex")); 
users.add(new User("Alex")); 
System.out.println(users.size());