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POHow to do test on Item selected In JCombobox
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copied!<p>I want refomuler my subject clearly, because it was not clear.</p> <p>so i have two JCombobox. if i choice a item in the first the second display the items.</p> <p>the first and the second JCombobox are fill with request from mysql, </p> <p>i create two methode, </p> <p>One to fill the first JCombobox : </p> <p>Code :</p> <pre><code>public void fillJCBOXPrj( ) { connexion c = new connexion(); Statement s ; ResultSet rs ; try { s = c.createStatement(); rs =c.selection("SELECT Distinct(IdProjet),idpro,NomProjet FROM projet where projet.iduser='"+this.getid()+"' "); while(rs.next()) { String num = rs.getString("idpro"); String nom = rs.getString("NomProjet"); String ref = rs.getString("IdProjet"); jComboBox1.addItem(new RF(nom,ref,num)); } } catch (Exception ex) { ex.printStackTrace(); } } </code></pre> <p>the sconde methode : fill the seconde JCombobox dependent on the Selected Item in first JCombobox</p> <pre><code>Code : public void fillJCBOXActivite() { RF n = (RF) jComboBox1.getSelectedItem(); connexion c = new connexion(); Statement s ; ResultSet rs ; try { s = c.createStatement(); System.out.println(n.num); rs =c.selection("SELECT idactiv,NomActiviter,Phase FROM activiter WHERE activiter.IDProjet='"+n.num+"' "); while(rs.next()) { String num = rs.getString("idactiv"); String nom = rs.getString("NomActiviter"); String ref = rs.getString("Phase"); jComboBox3.addItem(new RF(nom,ref,num)); } } catch (Exception ex) { ex.printStackTrace(); } } </code></pre> <p>and <code>RF n = (RF) jComboBox1.getSelectedItem();</code> it call class RF to return the 'num' of selected item in the first JCombobox Which used in request,</p> <pre><code>RF **n** = (RF) jComboBox1.getSelectedItem(); ..... .... rs =c.selection("SELECT idactiv,NomActiviter,Phase FROM activiter WHERE activiter.IDProjet=**'"+n.num+"'** "); </code></pre> <p>Class RF :</p> <pre><code>class RF { public final String nom; public final String ref; public final String num; public RF(String nom, String ref, String num) { this.nom = nom; this.num = num; this.ref = ref; } @Override public String toString() { return ref +" - " +nom ; } } </code></pre> <p>and finally i do call the methodes when application start, so i do this ,</p> <p>private void formWindowOpened(java.awt.event.WindowEvent evt) { </p> <p>fillJCBOXPrj(); fillJCBOXActivite();</p> <p>} </p> <p>But the probleme is, if i dont have any Item in the first JCombobx ( no data in DataBase Table) then it give a error in this line </p> <p>i guess the error come from 'n.num' </p> <pre><code>java.lang.NullPointerException at UserFrame.fillJCBOXActivite(UserFrame.java:202) </code></pre> <p>so want to do test on n.num that to do nothing if the first JCombobox dont have Items </p> <p>Thanks for help and i hope is clear now cause am not good in Anglish </p>

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