fabio valsecchi [https://community.jboss.org/people/fabiovalse] created the discussion "Entity hashCode and equals overriding" To view the discussion, visit: https://community.jboss.org/message/786963#786963 -------------------------------------------------------------- Hi there, I'm having some problems overring hashCode() and equals() methods of an entity Book. This is my code: ------------------------------------------------------------------------ @Override public int hashCode() { int hash = 1;               hash = hash * 31 + this.isbn.hashCode(); return hash;           } @Override public boolean equals(Object o) { if (o==this) return true; if (o instanceof Book) { return (this.isbn == ((Book) o).getIsbn());              }              return false;           } ------------------------------------------------------------------------ The problem is that when I try to add a book to a hashMap like here: ------------------------------------------------------------------------ @Override public void addArticle(Book book, Integer quantity) {               Integer *currentQuantity* = cart.getArticles().get(book);               System.out.println(currentQuantity); if (currentQuantity == null) {                   currentQuantity = 0;         }         currentQuantity += quantity; cart.getArticles().put(book, currentQuantity);     } ------------------------------------------------------------------------ The *currentQuantity* Integer is always null even if in the hashMap there's already the Book that i'm adding. Maybe it's a problem of my hashCode and equals implementation but i've tried using a hashCode() that return always 1 and with an equals that return always true and *currentQuantity* is still null. Can someone give me a hint? Thank you in advance -------------------------------------------------------------- Reply to this message by going to Community [https://community.jboss.org/message/786963#786963] Start a new discussion in EJB3 Development at Community [https://community.jboss.org/choose-container!input.jspa?contentType=1&...]