title: Exception in thread “AWT-EventQueue-0” java.lang.NullPointerException on click on JButton to INSERT IN DATABASE
body: <p>I am new to java and JDBC usage. I am writing my first java application that connects to database. But i am getting this error when i click on th JButton that performs the INSERT. But i get this error:</p>
  <pre><code>Exception in thread &quot;AWT-EventQueue-0&quot; java.lang.NullPointerException
      at controlbiblioteca.Conexion.execute(Conexion.java:39)
      at controlbiblioteca.InsertarPrestamo.btnInsertarActionPerformed(InsertarPrestamo.java:96)
      at controlbiblioteca.InsertarPrestamo.access$000(InsertarPrestamo.java:9)
      at controlbiblioteca.InsertarPrestamo$1.actionPerformed(InsertarPrestamo.java:66)
      at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
      at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
      at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
      at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
      at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
      at java.awt.Component.processMouseEvent(Component.java:6533)
      at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
      at java.awt.Component.processEvent(Component.java:6298)
      at java.awt.Container.processEvent(Container.java:2236)
      at java.awt.Component.dispatchEventImpl(Component.java:4889)
      at java.awt.Container.dispatchEventImpl(Container.java:2294)
      at java.awt.Component.dispatchEvent(Component.java:4711)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
      at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
      at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
      at java.awt.Container.dispatchEventImpl(Container.java:2280)
      at java.awt.Window.dispatchEventImpl(Window.java:2746)
      at java.awt.Component.dispatchEvent(Component.java:4711)
      at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
      at java.awt.EventQueue.access$500(EventQueue.java:97)
      at java.awt.EventQueue$3.run(EventQueue.java:709)
      at java.awt.EventQueue$3.run(EventQueue.java:703)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
      at java.awt.EventQueue$4.run(EventQueue.java:731)
      at java.awt.EventQueue$4.run(EventQueue.java:729)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
      at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
      at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
  </code></pre>
  <p>In Conexion.java:39 i have this:</p>
  <pre><code>Statement instruccion;
          try {
              instruccion = myConn.createStatement();   //line39
              instruccion.executeUpdate(sql);
              
          } catch (SQLException ex) {
              JOptionPane.showMessageDialog(null,&quot;Error al ejecutar la instruccion&quot;);
              System.out.println(ex);
              System.exit(0);
              
          }
  </code></pre>
  <p>In the Jbutton i wrote this code.</p>
  <pre><code>if(txtIDuser.getText().isEmpty()|| txtIDejemplar.getText().isEmpty()|| txtFechpres.getText().isEmpty()|| txtFechdev.getText().isEmpty())
          {
              JOptionPane.showMessageDialog(null,&quot;Favor de llenar todos los campos&quot;);
          }        
          else
          {
              Conexion c = new Conexion();
              c.execute(&quot;INSERT INTO prestamo VALUES (&quot;+txtIDuser.getText()+&quot;, &quot;+txtIDejemplar.getText()+&quot;, '&quot;+txtFechpres.getText()+&quot;', '&quot;+txtFechdev.getText()+&quot;' );&quot;);
              JOptionPane.showMessageDialog(null,&quot;Insercion realizada correctamente&quot;,&quot;Exito!&quot;,JOptionPane.INFORMATION_MESSAGE);
          }
  </code></pre>
  <p>And in the class named Bibliotecaria the private connection variable is not used apparently.
  <a href="https://i.stack.imgur.com/D1HIo.png" rel="nofollow noreferrer">enter image description here</a></p>