Need Help With Button Events

**adlb1300** · 11-02-2007, 06:59 PM

I'm trying to create an application that utilizes a form to gather info from the user. The form has 4 buttons - start, exit, clear and search. I'm trying to program the appropriate actions for these buttons but no matter what I also have an error. When I have tried to compile I get and error to the effect that the variable is non-static and cannot be run.

Can anybody help me out?

Java Code:

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

public class FlightInterface {

     
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        JLabel title = new JLabel("Flight Info");
        title.setFont(new Font("Serif", Font.BOLD, 30));
        JPanel bannerPanel = new JPanel();
        bannerPanel.setPreferredSize(new Dimension(300, 50));
        bannerPanel.add(title);
        
        JTextField nameInputField = new JTextField();
        JLabel inputAirlineName = new JLabel("Airline Name:     ");
        inputAirlineName.setFont(new Font("Serif", Font.PLAIN, 14));
        JPanel namePanel = new JPanel();
        namePanel.setLayout(new BoxLayout(namePanel, BoxLayout.X_AXIS));
        namePanel.setPreferredSize(new Dimension(200, 20));
        namePanel.add(inputAirlineName);
        namePanel.add(nameInputField);
        
        JLabel inputFlightNum = new JLabel("Flight Number:   ");
        inputFlightNum.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField flightNumField = new JTextField();          
        JPanel flightNumPanel = new JPanel();
        flightNumPanel.setLayout(new BoxLayout(flightNumPanel, BoxLayout.X_AXIS));
        flightNumPanel.setPreferredSize(new Dimension(200, 20));
        flightNumPanel.add(inputFlightNum);
        flightNumPanel.add(flightNumField);
        
        JLabel inputOrigin = new JLabel("City of Origin:    ");
        inputOrigin.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField originField = new JTextField();          
        JPanel originPanel = new JPanel();
        originPanel.setLayout(new BoxLayout(originPanel, BoxLayout.X_AXIS));
        originPanel.setPreferredSize(new Dimension(200, 20));
        originPanel.add(inputOrigin);
        originPanel.add(originField);
        
        JLabel inputDestination = new JLabel("Destination City: ");
        inputDestination.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField destinationField = new JTextField();          
        JPanel destinationPanel = new JPanel();
        destinationPanel.setLayout(new BoxLayout(destinationPanel, BoxLayout.X_AXIS));
        destinationPanel.setPreferredSize(new Dimension(200, 20));
        destinationPanel.add(inputDestination);
        destinationPanel.add(destinationField);
        
        JPanel blankPanel = new JPanel();
        blankPanel.setLayout(new BoxLayout(blankPanel, BoxLayout.X_AXIS));
        blankPanel.setPreferredSize(new Dimension(200, 20));
        
        JButton startButton = new JButton("Get Data");
        startButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton exitButton = new JButton("Exit");
        exitButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton searchButton = new JButton("Search");
        searchButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton clearButton = new JButton("Clear");
        clearButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new BoxLayout(buttonPanel, BoxLayout.X_AXIS));
        buttonPanel.setPreferredSize(new Dimension(250, 20));
        buttonPanel.add(startButton);
        buttonPanel.add(clearButton);
        buttonPanel.add(searchButton);
        buttonPanel.add(exitButton);
        
              
        JPanel mainPanel = new JPanel();
        mainPanel.add(bannerPanel, BorderLayout.NORTH);
        mainPanel.add(namePanel, BorderLayout.CENTER);
        mainPanel.add(flightNumPanel, BorderLayout.CENTER);
        mainPanel.add(originPanel, BorderLayout.CENTER);
        mainPanel.add(destinationPanel, BorderLayout.CENTER);
        mainPanel.add(blankPanel, BorderLayout.CENTER);
        mainPanel.add(buttonPanel, BorderLayout.SOUTH);
        
        JFrame f = new JFrame(); // creates new instance of JFrame so graph can be displayed
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // tells JFrame to close on exit
        f.getContentPane().add(mainPanel);
        f.setSize(300, 265); // sets size of JFrame
        f.setLocation(200, 200); // sets location of JFrame
        f.setVisible(true); // makes JFrame visible
        
             
    } // end main
    
} // end class

Thanks

**hardwired** · 11-02-2007, 08:04 PM

Your code compiles and runs okay. Here's a suggestion.

Java Code:

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

public class FI {
    private JPanel getContent() {
        JLabel title = new JLabel("Flight Info");
        title.setFont(new Font("Serif", Font.BOLD, 30));
        JPanel bannerPanel = new JPanel();
        bannerPanel.setPreferredSize(new Dimension(300, 50));
        bannerPanel.add(title);
        
        JTextField nameInputField = new JTextField();
        JLabel inputAirlineName = new JLabel("Airline Name:     ");
        inputAirlineName.setFont(new Font("Serif", Font.PLAIN, 14));
        JPanel namePanel = new JPanel();
        namePanel.setLayout(new BoxLayout(namePanel, BoxLayout.X_AXIS));
        namePanel.setPreferredSize(new Dimension(200, 20));
        namePanel.add(inputAirlineName);
        namePanel.add(nameInputField);
        
        JLabel inputFlightNum = new JLabel("Flight Number:   ");
        inputFlightNum.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField flightNumField = new JTextField();          
        JPanel flightNumPanel = new JPanel();
        flightNumPanel.setLayout(new BoxLayout(flightNumPanel, BoxLayout.X_AXIS));
        flightNumPanel.setPreferredSize(new Dimension(200, 20));
        flightNumPanel.add(inputFlightNum);
        flightNumPanel.add(flightNumField);
        
        JLabel inputOrigin = new JLabel("City of Origin:    ");
        inputOrigin.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField originField = new JTextField();          
        JPanel originPanel = new JPanel();
        originPanel.setLayout(new BoxLayout(originPanel, BoxLayout.X_AXIS));
        originPanel.setPreferredSize(new Dimension(200, 20));
        originPanel.add(inputOrigin);
        originPanel.add(originField);
        
        JLabel inputDestination = new JLabel("Destination City: ");
        inputDestination.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField destinationField = new JTextField();          
        JPanel destinationPanel = new JPanel();
        destinationPanel.setLayout(new BoxLayout(destinationPanel, BoxLayout.X_AXIS));
        destinationPanel.setPreferredSize(new Dimension(200, 20));
        destinationPanel.add(inputDestination);
        destinationPanel.add(destinationField);

        JPanel blankPanel = new JPanel();
        blankPanel.setLayout(new BoxLayout(blankPanel, BoxLayout.X_AXIS));
        blankPanel.setPreferredSize(new Dimension(200, 20));

        JButton startButton = new JButton("Get Data");
        startButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton exitButton = new JButton("Exit");
        exitButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton searchButton = new JButton("Search");
        searchButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton clearButton = new JButton("Clear");
        clearButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new BoxLayout(buttonPanel, BoxLayout.X_AXIS));
//        buttonPanel.setPreferredSize(new Dimension(250, 20));
        buttonPanel.add(startButton);
        buttonPanel.add(clearButton);
        buttonPanel.add(searchButton);
        buttonPanel.add(exitButton);

        JPanel mainPanel = new JPanel();
        System.out.println("JPanel default layout manager = " +
                            mainPanel.getLayout().getClass().getName());
        mainPanel.add(bannerPanel, BorderLayout.NORTH);
        mainPanel.add(namePanel, BorderLayout.CENTER);
        mainPanel.add(flightNumPanel, BorderLayout.CENTER);
        mainPanel.add(originPanel, BorderLayout.CENTER);
        mainPanel.add(destinationPanel, BorderLayout.CENTER);
        mainPanel.add(blankPanel, BorderLayout.CENTER);
        mainPanel.add(buttonPanel, BorderLayout.SOUTH);
        return mainPanel;
    }

    public static void main(String[] args) {
        // Using the variable "app" will help avoid problems
        // with the static modifier in your class.
        FI app = new FI();
        // creates new instance of JFrame so graph can be displayed
        JFrame f = new JFrame();
        // tells JFrame to close on exit
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(app.getContent());
        f.setSize(300, 265);      // sets size of JFrame
        f.setLocation(200, 200);  // sets location of JFrame
        f.setVisible(true);       // makes JFrame visible
    } // end main
} // end class

**adlb1300** · 11-02-2007, 08:11 PM

Hardwired,

I will give it a try. Thanks for the tip. I'm starting to get it as I actually handcoded the form which I was quite impressed with myself for.

**adlb1300** · 11-02-2007, 09:07 PM

Hardwired,

I'm still getting error messages but at least they are different ones. Here is the code I have. I'm just trying to code the exit button first and once I figured that out I thought I would add in the others.

Java Code:

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

public class FlightInterface {
    
    private JPanel getContent() {
        
        JLabel title = new JLabel("Flight Info");
        title.setFont(new Font("Serif", Font.BOLD, 30));
        JPanel bannerPanel = new JPanel();
        bannerPanel.setPreferredSize(new Dimension(300, 50));
        bannerPanel.add(title);
        
        JTextField nameInputField = new JTextField();
        JLabel inputAirlineName = new JLabel("Airline Name:     ");
        inputAirlineName.setFont(new Font("Serif", Font.PLAIN, 14));
        JPanel namePanel = new JPanel();
        namePanel.setLayout(new BoxLayout(namePanel, BoxLayout.X_AXIS));
        namePanel.setPreferredSize(new Dimension(200, 20));
        namePanel.add(inputAirlineName);
        namePanel.add(nameInputField);
        
        JLabel inputFlightNum = new JLabel("Flight Number:   ");
        inputFlightNum.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField flightNumField = new JTextField();
        JPanel flightNumPanel = new JPanel();
        flightNumPanel.setLayout(new BoxLayout(flightNumPanel, BoxLayout.X_AXIS));
        flightNumPanel.setPreferredSize(new Dimension(200, 20));
        flightNumPanel.add(inputFlightNum);
        flightNumPanel.add(flightNumField);
        
        JLabel inputOrigin = new JLabel("City of Origin:    ");
        inputOrigin.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField originField = new JTextField();
        JPanel originPanel = new JPanel();
        originPanel.setLayout(new BoxLayout(originPanel, BoxLayout.X_AXIS));
        originPanel.setPreferredSize(new Dimension(200, 20));
        originPanel.add(inputOrigin);
        originPanel.add(originField);
        
        JLabel inputDestination = new JLabel("Destination City: ");
        inputDestination.setFont(new Font("Serif", Font.PLAIN, 14));
        JTextField destinationField = new JTextField();
        JPanel destinationPanel = new JPanel();
        destinationPanel.setLayout(new BoxLayout(destinationPanel, BoxLayout.X_AXIS));
        destinationPanel.setPreferredSize(new Dimension(200, 20));
        destinationPanel.add(inputDestination);
        destinationPanel.add(destinationField);
        
        JPanel blankPanel = new JPanel();
        blankPanel.setLayout(new BoxLayout(blankPanel, BoxLayout.X_AXIS));
        blankPanel.setPreferredSize(new Dimension(200, 20));
        
        JButton startButton = new JButton("Get Data");
        startButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton exitButton = new JButton("Exit");
        exitButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton searchButton = new JButton("Search");
        searchButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JButton clearButton = new JButton("Clear");
        clearButton.setFont(new Font("Serif", Font.PLAIN, 14));
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new BoxLayout(buttonPanel, BoxLayout.X_AXIS));
        buttonPanel.add(startButton);
        buttonPanel.add(clearButton);
        buttonPanel.add(searchButton);
        buttonPanel.add(exitButton);
        
        exitButton.addActionListener(this);
               
        JPanel mainPanel = new JPanel();
        System.out.println("JPanel default layout manager = " +
                mainPanel.getLayout().getClass().getName());
        mainPanel.add(bannerPanel, BorderLayout.NORTH);
        mainPanel.add(namePanel, BorderLayout.CENTER);
        mainPanel.add(flightNumPanel, BorderLayout.CENTER);
        mainPanel.add(originPanel, BorderLayout.CENTER);
        mainPanel.add(destinationPanel, BorderLayout.CENTER);
        mainPanel.add(blankPanel, BorderLayout.CENTER);
        mainPanel.add(buttonPanel, BorderLayout.SOUTH);
        return mainPanel;
    }
    
    public void actionPerformed(ActionEvent e){
        if(e.getSource() == exitButton){
            System.exit(0);
        }
     
    }
    
    public static void main(String[] args) {
        // Using the variable "app" will help avoid problems
        // with the static modifier in your class.
        FlightInterface app = new FlightInterface();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(app.getContent());
        f.setSize(300, 265);      // sets size of JFrame
        f.setLocation(200, 200);  // sets location of JFrame
        f.setVisible(true);       // makes JFrame visible
    } // end main
}

Here are the error messages that I get:

E:\Intro OOP\FlightInterface\src\flightinterface\FlightInte rface.java:84: illegal start of expression
public void actionPerformed(ActionEvent e){
E:\Intro OOP\FlightInterface\src\flightinterface\FlightInte rface.java:89: ';' expected
}

Thanks for your help

**hardwired** · 11-02-2007, 10:39 PM

I copied, pasted (into a new folder) and compiled your last posted code and got these in the console:

Java Code:

C:\jexp\flightInterface>javac FlightInterface.java
FlightInterface.java:84: cannot find symbol
symbol  : class ActionEvent
location: class FlightInterface
    public void actionPerformed(ActionEvent e){
                                ^
FlightInterface.java:69: addActionListener(java.awt.event.ActionListener) in jav
ax.swing.AbstractButton cannot be applied to (FlightInterface)
        exitButton.addActionListener(this);
                  ^
FlightInterface.java:85: cannot find symbol
symbol  : variable exitButton
location: class FlightInterface
        if(e.getSource() == exitButton){
                            ^
3 errors

Make the following changes to compile and run okay:

Java Code:

// Add import statement.
import java.awt.event.*;

// Implement ActionListener so "this" can be an ActionListener
public class FlightInterface implements ActionListener {
    // Declare exitButton as a member variable.
    // This puts it in class scope where it can be
    // accessed inside the actionPerformed method.
    JButton exitButton;

        startButton.setFont(new Font("Serif", Font.PLAIN, 14));
        // Remove the type declaration from the instantiation so
        // that exitButton is not a local variable hiding the
        // member variable (of the same name) which would remain
        // uninstantiated and thus have a value of null, causing
        // NullPointerExceptions when you try to access it in
        // the actionPerformed method.
        exitButton = new JButton("Exit");

I did not get the compile errors you reported. The console errors give the line number of the trouble to help track it down. Maybe you omitted a semi-colon somewhere above the actionPerformed method.

**adlb1300** · 11-03-2007, 05:36 AM

Hardwired once again you come through for me. I had the closing bracket for the JPanel method after the ActionPerformed method instead of before. I changed that and made the changes you suggested before and now it works. Thanks

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