Java swing standards dialog box implementation

package test001;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JToolBar;
public class TestJOptionPane implements ActionListener{
    private JFrame jf = new JFrame(" Standard dialog box testing ");
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        new TestJOptionPane().createUI();
    }
    public void createUI(){
        JToolBar jtb = new JToolBar();
        String[] s = {" error ", " Exit the confirmation 1", " Exit the confirmation 2", " warning ", " The input ", " choose "};
        int size = s.length;
        JButton[] button = new JButton[size];
        for(int i = 0; i < size; i++){
            button[i] = new JButton(s[i]);
            button[i].addActionListener(this);
            jtb.add(button[i]);
        }
        jf.add(jtb, "North");
        jf.setSize(350, 150);
        jf.setLocation(400, 200);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setVisible(true);
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        String s = e.getActionCommand();
        if(s.equals(" error ")){
            JOptionPane.showMessageDialog(null, " Error message to display ---",
                    " Error message ",JOptionPane.ERROR_MESSAGE);
        }
        else if(s.equals(" Exit the confirmation 1")){
            int result = JOptionPane.showConfirmDialog(null, 
                    " Is the program saved before rollout? ");
            if(result == JOptionPane.YES_OPTION){
                System.out.println(" Save the program ---");
                System.exit(0);
            }
            else if(result == JOptionPane.NO_OPTION){
                System.exit(0);
            }
        }
        else if(s.equals(" Exit the confirmation 2")){
            int result = JOptionPane.showConfirmDialog(null, " Do you save the program before exiting? ");
            if(result == JOptionPane.YES_OPTION){
                System.out.println(" Save the program ---");
                System.exit(0);
            }
            else if(result == JOptionPane.NO_OPTION){
                System.exit(0);
            }
        }
        else if(s.equals(" warning ")){
            Object[] options = {" Continue to ", " undo "};
            int result = JOptionPane.showOptionDialog(null,
                    " This operation may result in data loss ","Warning", JOptionPane.DEFAULT_OPTION,
                    JOptionPane.WARNING_MESSAGE, null, options, options[0]);
            if(result == 0){
                System.out.println(" Continue to operate ---");
            }
        }
        else if(s.equals(" The input ")){
            String name = JOptionPane.showInputDialog(" Please enter your name: ");
            if(name != null){
                System.out.println(" Name: " + name);
            }
        }
        else if(s.equals(" choose ")){
            Object[] possibleValues = {" sports ", " political ", " economic ", " culture "};
            Object selectedValue = JOptionPane.showInputDialog(null, 
                    "Choose one","Input", JOptionPane.INFORMATION_MESSAGE, null,
                    possibleValues, possibleValues[0]);
            String choose = (String)selectedValue;
            if(choose != null){
                System.out.println(" What you choose is: "+ choose);
            }
        }
    }
}