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Passing a parameter to Constructor error

1 reply on 1 page. Most recent reply: Apr 14, 2004 11:48 AM by twc

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Ja Ja Binks

Posts: 14
Nickname: ds99bwood9
Registered: Apr, 2004

Passing a parameter to Constructor error

Posted: Apr 14, 2004 7:37 AM

Hi, I have a cannot resolve symbol error when I pass the parameter (ActionListener listener) to the Constructor for a GUI Vcr interface that I am developing. Can anyone see where I am going wrong?

PROGRAMMINGLISTING.JAVA

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

class ProgrammeListing extends JFrame implements ActionListener
{

public ProgrammeListing(ActionListener listener)
{
setLocation(20,20);
setSize(800,600);

JPanel myPanel = new JPanel();
myPanel.setLayout(null);
setContentPane(myPanel);

JButton exitButton = new JButton("Exit");
exitButton.setBounds(20,40,70,30);
exitButton.setBackground(Color.red);
exitButton.addActionListener(this);
myPanel.add(exitButton);

setVisible(true);
} //constructor

public boolean validSelection()
{
}

public int getDay()
{
}

public int getMonth()
{
}

public String getChannel()
{
}

public int getStartHour()
{
}

public int getStartMin()
{
}

public int getStopHour()
{
}

public int getStopMin()
{
}

public String getTitle()
{
}

public void actionPerformed(ActionEvent e)
{
if (e.getSource() instanceof JButton)
{
System.out.println("Closing window");
System.exit(0);
}
}
}

and....

VCR.JAVA

class Vcr
{
public static void main(String args[])
{
ProgrammeListing vcr = new ProgrammeListing();
} // main
} // class Vcr

I am aware this may be a very basic error but my java isn't so great and I am looking to develop it, seeing as though my degree is Computer Science...

twc

Posts: 129
Nickname: twc
Registered: Feb, 2004

Re: Passing a parameter to Constructor error

Posted: Apr 14, 2004 11:48 AM

The main problem is that you are not sending the ActionListener as an argument in the VCR class. However, you do not need the ActionListener as a parameter so the easiest thing to do is to change your constructor heading to the following.

public ProgrammeListing()

However, let me suggest a more OO way to handle events. Notice the use of an inner class to handle the event.

PROGRAMMINGLISTING.JAVA
 
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.event.*;
 
class ProgrammeListing extends JFrame
{
  public ProgrammeListing()
  {
    setLocation(20,20);
    setSize(800,600);
 
    JPanel myPanel = new JPanel();
    myPanel.setLayout(null);
    setContentPane(myPanel);
 
    JButton exitButton = new JButton("Exit");
    exitButton.setBounds(20,40,70,30);
    exitButton.setBackground(Color.red);
    exitButton.addActionListener(new ExitListener());
    myPanel.add(exitButton);
 
    setVisible(true);
  } //constructor
 
  //snipped empty methods for brevity
 
  class ExitListener implements ActionListener//inner class
  {
    public void actionPerformed(ActionEvent e)
    {
       System.out.println("Closing window");
       System.exit(0);
    }
  }
}

BTW, JFrame's have a setDefaultCloseOperation() method that will control the close button on the frame. (The X button on Windows and Mac's)

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