Thread: Newbie Java problem --->"Cannot make a static reference to the non-static field data"

Hey so I've been working on a lab for my intro to software developing class and have been trying to get my program to work for hours since yesterday morning. It's a real basic program, im sure someone will be able to figure out the issue im having. Hopefully once I learn what I'm doing I'll be able to return the favor, but until then thanks, heres the code.

I bolded the errors which happen when I try to reference the non static variable in my main method which i know doesnt work, but I cant seem to get it, there are always either errors, the program freezes, or just completely does nothing. Any help is appreciated, thanks!

package lab8;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Scanner;
 
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
 
@SuppressWarnings("serial")
public class GUIMonthNames extends JFrame {
	private JLabel instructions;
	private JTextField data;
	public GUIMonthNames() {		
		  super("Month Names: GUI version");
		  setSize(400,400);
		  setDefaultCloseOperation(EXIT_ON_CLOSE);
		  Container myPane = getContentPane();
		  myPane.setLayout(new FlowLayout());
		  instructions = new JLabel("Enter a number (1-12) below");
		  data = new JTextField(20);
		  add(data);
		  add(instructions);
		  setVisible(true);	
		}
 
 
	public static void main(String[] args) {
				new GUIMonthNames();
 
			[B]data[/B].addActionListener(new ActionListener() {	
				public void actionPerformed(ActionEvent e) {
					Scanner keyboard = new Scanner(System.in);
					int monthNumber = keyboard.nextInt();
					monthNumber = new Integer([B]data[/B].getText());
					final String MONTH_TABLE = "January  February March    April    May      June     " +
							"July     August   SeptemberOctober  November December ";
					int start = (monthNumber - 1) * 9;
					int stop = start + 9;
					String monthName = MONTH_TABLE.substring(start, stop);
					[B]data[/B].setText(monthNumber +	" is '" + monthName.trim() + "'.");	
				}
 
		});	
 
}}

Static things (variables, methods, classes, etc) are things that don't belong to a particular instance of a class. For example, JFrame.EXIT_ON_CLOSE doesn't care which instance of JFrame it belongs to, because it's always going to be and mean the same thing. That's why the main method is always static- it doesn't belong to a particular instance of the class it's in.

Your data variable is not static, so it belongs to a particular instance of your class. If you create two instances of your GUIMonthNames class, you're going to have two data variables that refer to two completely different things. But you'll still only have one main class, since it does not belong to any particular instance.

So, when you're in the main method, you aren't in any particular instance of GUIMonthNames- so which data variable should it access? That's what that error means. To fix it, look at what you're doing with your constructor- you're creating an instance of GUIMonthNames, but then you aren't doing anything with it.

hey thanks for the quick reply, I tried to fix what you suggested.

Now there are no errors and I tried to create an instance for GUIMonthNames called MonthNames, then I used the instance to reference my non static variable. No errors but no dice. Is it a syntax problem or something larger, help please!

package lab8;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Scanner;
 
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
@SuppressWarnings("serial")
 
public class GUIMonthNames extends JFrame {
	private JLabel instructions;
	private JTextField data;
 
	public GUIMonthNames() {		
		  super("Month Names: GUI version");
		  setSize(400,400);
		  setDefaultCloseOperation(EXIT_ON_CLOSE);
		  Container myPane = getContentPane();
		  myPane.setLayout(new FlowLayout());
		  instructions = new JLabel("Enter a number (1-12) below");
		  data = new JTextField(20);
		  setVisible(true);	
		  add(instructions);
		  add(data);
		}	
 
	public static void main(String[] args) {
			new GUIMonthNames();
			final GUIMonthNames monthNames = new GUIMonthNames();
			monthNames.data.addActionListener(new ActionListener()
			 {	
				public void actionPerformed(ActionEvent e) {
					int	monthNumber = new Integer(monthNames.data.getText());
					Scanner keyboard = new Scanner(System.in);
					monthNumber = keyboard.nextInt();
					final String MONTH_TABLE = "January  February March    April    May      June     " +
							"July     August   SeptemberOctober  November December ";
					int start = (monthNumber - 1) * 9;
					int stop = start + 9;
					String monthName = MONTH_TABLE.substring(start, stop);
					monthNames.data.setText(monthNumber +	" is '" + monthName.trim() + "'.");	
				}
 
	});
 
}}

You could also use a getter function.

But why are you doing any of that from main in the first place?