Accumulated sum using swing

Problem: Calculate the sum of the current input with the sum of past inputs. You may have:

1. JLabel: "Enter an integer"
2. JTextField: for accepting user input
3. JLabel: "Accumulated sum is"
4. JTextField (non-editable): for displaying the accumulated sum

The program shall accumulate the number entered in the input textfield and display the sum in the output textfield.

Solution: Although no button was specified as a component, the problem didn't specify when to accept input, so to avoid headaches we will accept the input when the button is clicked. Once the button is clicked the current input will be added to previous inputs and be shown in the output textfield. If the input is invalid (not a number) then the input will be ignored. The button click code is shown bellow:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // go button clicked
        long current = 0;
        try{
            current = Long.parseLong(inputTextField.getText());
        }catch(NumberFormatException e){
            // invalid input (not a number)
            System.out.println("Invalid input");
            return;
        }
        
        currentSum +=current;
        
        outputTextField.setText(currentSum+"");
        
    }

GUI:

Complete code and layout (generated by NetBeans):

package accumulatedsum;


/**
 *
 * @author oscartorres
 */
public class MainFrame extends javax.swing.JFrame {
    long currentSum = 0;


    /**
     * Creates new form MainFrame
     */
    public MainFrame() {
        initComponents();
    }


    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    // created by NetBeans
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {


        jLabel1 = new javax.swing.JLabel();
        inputTextField = new javax.swing.JTextField();
        jLabel2 = new javax.swing.JLabel();
        outputTextField = new javax.swing.JTextField();
        jButton1 = new javax.swing.JButton();


        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);


        jLabel1.setText("Enter an integer");


        jLabel2.setText("Accumulated sum is");


        outputTextField.setEditable(false);
        outputTextField.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                outputTextFieldActionPerformed(evt);
            }
        });


        jButton1.setText("Go");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });


        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jLabel2)
                    .addComponent(jLabel1))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                    .addComponent(inputTextField, javax.swing.GroupLayout.DEFAULT_SIZE, 84, Short.MAX_VALUE)
                    .addComponent(outputTextField))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(jButton1))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(inputTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jLabel1)
                    .addComponent(jButton1))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel2)
                    .addComponent(outputTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );


        pack();
    }// </editor-fold>                        


    private void outputTextFieldActionPerformed(java.awt.event.ActionEvent evt) {                                                
        // TODO add your handling code here:
    }                                               


    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // go button clicked
        long current = 0;
        try{
            current = Long.parseLong(inputTextField.getText());
        }catch(NumberFormatException e){
            // invalid input (not a number)
            System.out.println("Invalid input");
            return;
        }
        
        currentSum +=current;
        
        outputTextField.setText(currentSum+"");
        
    }                                        


    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>


        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new MainFrame().setVisible(true);
            }
        });
    }


    // Variables declaration - do not modify                     
    private javax.swing.JTextField inputTextField;
    private javax.swing.JButton jButton1;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JTextField outputTextField;
    // End of variables declaration                   
}