Java GUI, button gives the number of +1 and -1 to textfield

Question

I have homework with Java GUI, and i'm a new with java programming. Anyone can help my problems ?.

my screenshot : http://cdn.kaskus.com/images/2014/03/21/2556566_20140321011737.png

If I press the "+" button, the Textfield will show numbers 0,1,2,3,4,5,6,... and if I press "-" button, the textfield will decrease the numbers properly, but not below 0. Here is my source code:

    package Main.Code;

public class NewJFrame extends javax.swing.JFrame {

    public NewJFrame() {
        initComponents();
    }

    @SuppressWarnings("unchecked")                         
    private void initComponents() {

        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jTextField1 = new javax.swing.JTextField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jButton1.setText("-");

        jButton2.setText("+");

        jTextField1.setHorizontalAlignment(javax.swing.JTextField.CENTER);
        jTextField1.setText("0");
        jTextField1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jTextField1ActionPerformed(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()
                .addGap(68, 68, 68)
                .addComponent(jButton1)
                .addGap(18, 18, 18)
                .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 41, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addComponent(jButton2)
                .addContainerGap(68, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(101, 101, 101)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jButton2)
                    .addComponent(jButton1))
                .addContainerGap(80, Short.MAX_VALUE))
        );

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

    private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:
    }                                           

    public static void main(String args[]) {
        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(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }

        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }

    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JTextField jTextField1;                  
}

Answer 1

Try This :

      class NewJFrame extends javax.swing.JFrame implements ActionListener {
      int total=0;
      /*...
      ....
      code ...
     */
    jButton1.setText("-");
    jButton2.setText("+");
    jButton1.addActionListener(this);
    jButton2.addActionListener(this);

   }

Button Action Event Here :

   public  void  actionPerformed(ActionEvent e)
    {
        if(e.getSource()==jButton2)
                 { 
                    total +=1;
                    jTextField1.setText(""+total);
                 }     
        if(e.getSource()==jButton1)
                 { 
                    total -=1;
                    jTextField1.setText(""+total);
                 }  
      }