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Entity hashCode and equals overriding
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created by <a href="https://community.jboss.org/people/fabiovalse">fabio valsecchi</a> in <i>EJB3 Development</i> - <a href="https://community.jboss.org/message/786963#786963">View the full discussion</a>
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<div class="jive-rendered-content"><p>Hi there,</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>I'm having some problems overring hashCode() and equals() methods of an entity Book. This is my code:</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>------------------------------------------------------------------------</p><p class="p1">@Override</p><p class="p2">          <span class="s1">public</span> <span class="s1">int</span> hashCode() {</p><p class="p2">                    <span class="s1">int</span> hash = 1;</p><p class="p2">              hash = hash * 31 + <span class="s1">this</span>.<span class="s2">isbn</span>.hashCode();</p><p class="p2">              <span class="s1">return</span> hash;</p><p class="p2">          }</p><p class="p1"><span class="s3"> </span>@Override</p><p class="p2">          <span class="s1">public</span> <span class="s1">boolean</span> equals(Object o) {</p><p class="p2">             <span class="s1">if</span> (o==<span class="s1">this</span>)</p><p class="p2">                 <span class="s1">return</span> <span class="s1">true</span>;</p><p class="p2">             <span class="s1">if</span> (o <span class="s1">instanceof</span> Book) {</p><p class="p2">                 <span class="s1">return</span> (<span class="s1">this</span>.<span class="s2">isbn</span> == ((Book) o).getIsbn());</p><p class="p2">             }</p><p class="p3"><span class="s3">             </span>return<span class="s3"> </span>false<span class="s3">;</span></p><p class="p2">          }</p><p>------------------------------------------------------------------------</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>The problem is that when I try to add a book to a hashMap like here:</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>------------------------------------------------------------------------</p><p class="p1">@Override</p><p class="p2">    <span class="s1">public</span> <span class="s1">void</span> addArticle(Book book, Integer quantity) {</p><p class="p2">              Integer <strong>currentQuantity</strong> = <span class="s2">cart</span>.getArticles().get(book);</p><p class="p3">    </p><p class="p2">              System.<span class="s2">out</span>.println(currentQuantity);</p><p class="p3">     </p><p class="p2">        <span class="s1">if</span> (currentQuantity == <span class="s1">null</span>) {</p><p class="p2">                  currentQuantity = 0;</p><p class="p2">        }</p><p class="p2">        currentQuantity += quantity;</p><p class="p2">        <span class="s2">cart</span>.getArticles().put(book, currentQuantity);</p><p class="p2">    }</p><p>------------------------------------------------------------------------</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>The <strong>currentQuantity</strong> Integer is always null even if in the hashMap there's already the Book that i'm adding.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>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 <strong>currentQuantity</strong> is still null.</p><p>Can someone give me a hint?</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Thank you in advance</p></div>
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