Help with Building a GUI

Question

I'm trying to activate my buttons "Calculate" and "Exit" for my Box Volume Calculator GUI I created with NetBeans. I get the error message "if without else".
}// </editor-fold>//GEN-END:initComponents
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_jButton1ActionPerformed
if (evt.getSource()==btnCalculate)
               doCalculate();
               else if (evt.getSource()==btnExit)
                    System.exit(0);
          void doCalculate() {
          double height;
          double width;
          double depth;
          double volumeCalc;
          height =Double.parseDouble(txtHeight.getText());
          width =Double.parseDouble(txtWidth.getText());
          depth =Double.parseDouble(txtDepth.getText());
          volumeCalc =height*width*depth;
}//GEN-LAST:event_jButton1ActionPerformed
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_jButton2ActionPerformed
if (evt.getSource()==btnCalculate)
               doCalculate();
               else if (evt.getSource()==btnExit)
                    System.exit(0);
}//GEN-LAST:event_jButton2ActionPerformed
* @param args the command line arguments
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new BoxVolCalc().setVisible(true);
// Variables declaration - do not modify//GEN-BEGIN:variables
private javax.swing.JButton jButton1;
private javax.swing.JButton jButton2;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JPanel jPanel1;
private javax.swing.JTextField jTextField1;
private javax.swing.JTextField jTextField2;
private javax.swing.JTextField jTextField3;
private javax.swing.JTextField jTextField4;
// End of variables declaration//GEN-END:variables
}}}

Answer 1

Where is the error generated? It's perfectly legal to have an if without an else.
As an aside, why would you even put the duplicate if/else blocks in? You have two buttons and two listeners - you'd only need an if/else if you were dumb enough to wire all your listeners to all your buttons. Bizarre.