java addActionListener problem

[earthsiege]

hi guys,

iv written a prog which has a JtabbedPane GUI but the problem is on one of my tabs i have a JPanel called panel1. on panel1 i have a button called addButton now i add this button onto my panel and my panel onto the tab using the following code:

panel1.add(addButton);
tabbedPane.addTab("New Booking", null, panel1, "First Panel");

which works just fine and when compiled you see the tabs and the button on the first pane.

but then when i try and ad an actionlistener to the button using the following code:

  addButton.addActionListener(this);

i get this error:

PHP Code:

addActionListener(java.awt.event.ActionListener) in javax.swing.AbstractButton cannot be applied to (tester) 


tester is the name of my class.
can anyone help me?

[shmoove]

When you declare your class you need to specify that it implements the ActionListener interface:

class tester implements ActionListener {

otherwise the compiler won't know it can treat your class as an ActionListener and give you the error you mentioned when you try to pass it to a method that takes an ActionListener as a parameter.

shmoove

[earthsiege]

cant believ i missed that out.
thanks for the help man,
one more thing though, when im referring to the button in my actionPerformed class how do i refer to the addButton button?
i mean do i do this:

 public void actionPerformed(ActionEvent e){
        System.out.println(e.getSource());
    if(e.getSource() == addButton){...

or something else?

[turbowrx]

You got it. Happy programming.

[shmoove]

Yeah, as long as the addButton field is in scope in the actionPerformed() method (which it looks like it is, if it's a member of the tester class).

shmoove

[earthsiege]

ok....
not working...
i keep on getting the error:

cannot resolve symbol-addButton

i think im supposed to move the actionPerformer class so that its in scope bu im not sure where im supposed to move it to.
heres my code:

//GUI display for the tester program

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;


public class tester extends JFrame implements ActionListener{
    public tester()
        {
        super("Swimming Lesson Booking System");
        
        //create tabbed panel
        JTabbedPane tabbedPane = new JTabbedPane();
        //------------------------------------------------------------------------------------------------------------
        /*------------------------------------set up components for panel 1-----------------------------------------*/
        JLabel nameLabel = new JLabel("Name: ", SwingConstants.CENTER);
        JLabel surnameLabel = new JLabel("Surname: ", SwingConstants.CENTER);
        JLabel addressLabel = new JLabel("Address: ", SwingConstants.CENTER);
        JLabel guardianLabel = new JLabel("Name of guardian: ", SwingConstants.CENTER);
        JLabel paymentLabel = new JLabel("Payment method: ", SwingConstants.CENTER);
        JLabel classLabel = new JLabel("Level: ", SwingConstants.CENTER);
        JTextField nameText = new JTextField("", 10);
        JTextField surnameText = new JTextField("", 10);  
        JTextField guardianText = new JTextField("", 10);  
        JTextField addressText = new JTextField("", 10);
        JButton addButton = new JButton("Make new Booking");
        
        //setting up the different methods of payment
        String payments[]={"Cash", "Cheque", "Credit card"}; 
        
        //setting up the combo box
        JComboBox paymentMethod = new JComboBox(payments);
        paymentMethod.setMaximumRowCount(3);
        
        //Setting up the different classes available
        String classes[] = {"Ducklings Group A", "Ducklings Group B", "Beginners Group A ", "Beginners Group B ", "Beginners Group C ", "Intermediate", "Advanced"};
        
        //Setting up the swimming class combo box and adding the action event 
        JComboBox classesAvailable = new JComboBox(classes);
        classesAvailable.setMaximumRowCount(5);
        
           
        //adding components to the first panel
        JPanel panel1 = new JPanel();
        panel1.add(nameLabel);
        panel1.add(nameText);
        panel1.add(surnameLabel);
        panel1.add(surnameText);
        panel1.add(guardianLabel);
        panel1.add(guardianText);
        panel1.add(addressLabel);
        panel1.add(addressText);
        panel1.add(paymentLabel);
        panel1.add(paymentMethod);
        panel1.add(classLabel);
        panel1.add(classesAvailable);
        panel1.add(addButton);
        addButton.addActionListener(this);


        
        tabbedPane.addTab("New Booking", null, panel1, "First Panel");
        //-----------------------------------------------------------------------------------------------------
        /*-------------------------------------------------------set up panel 2-------------------------------*/
        JLabel viewLevelLabel = new JLabel("Level: ");
        JButton view = new JButton("View Bookings");
        
        //viewlevel combobox
        String viewClasses[] = {"All", "Ducklings", "Beginners", "Intermediate", "Advanced"};
        JComboBox viewClassesAvailable = new JComboBox(viewClasses);
        viewClassesAvailable.setMaximumRowCount(3);
        
        //panel 2
         JPanel panel2 = new JPanel();
         panel2.add(viewLevelLabel);
         panel2.add(viewClassesAvailable);
         panel2.add(view);
         
        
        tabbedPane.addTab("View Bookings", null, panel2, "Second Panel");
        
        
        
        /*------------------------------------------------------set up panel 3-------------------------------------*/
        JLabel deleteLabel = new JLabel("Please enter the refrence number of the\n booking you are looking to cancel");
        JTextField deleteText = new JTextField("",2);
        JButton deleteButton = new JButton("Cancel Booking");
        
        //panel3
        JPanel panel3 = new JPanel();
        panel3.add(deleteLabel);
        panel3.add(deleteText);
        panel3.add(deleteButton);
        
        tabbedPane.addTab("Cancel Booking", null, panel3, "Third Panel");        
        
        
        
        //------------------------------------------------------------------------------------------------------------
        //------------------------------------------------------------------------------------------------------------
        getContentPane().add(tabbedPane);
        
        setSize(400, 300);
        setVisible(true);
    }
    
    public static void main(String args[])
    {
        tester tabbedPaneDemo = new tester();
        tabbedPaneDemo.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    
    public void actionPerformed(ActionEvent e){
       // System.out.println(e.getSource());
    if(e.getSource() == addButton){ 
    Booking booking = new Booking(nameText.getText(), surnametext.getText(), guardianText.getText(),paymentMethod.getItemSelected(), addressText.getText(), classesAvailable.getItemSelected()); 
    }
}
}

[shmoove]

addButton is declared inside tester's constructor, so it's scope is only within that method. You can move the declaration outside of the constructor so it becomes a member field (so it's in scope in every method of the class):

public class tester extends JFrame implements ActionListener{
    JButton addButton;
    public tester()
        {
        // ....
        addButton = new JButton("Make new Booking");

or you could make the ActionListener an anonymous inner class within the constructor (so that the ActionListener is also in the same scope - inside the constructor):

public class tester extends JFrame {
    public tester()
      {
         // ....
         addButton.addActionListener(
              new ActionListener() {
                   public void actionPerformed(ActionEvent e){
                        // .....
                   }
              }
         );
       }

Notice that in this second case the tester class doesn't implement the interface anymore.

shmoove

[shmoove]

A tutorial about scope in Java.

shmoove