Thread: Warning on class with JFrame inheritance (extends)

I'll start off by showing my full code:

Main class

import javax.swing.JFrame;
 
public class groupingTest {
	public static void main (String[] args) {
		groupWindow test = new groupWindow();
 
		test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		test.setBounds(400, 400, 500, 100);
		test.setVisible(true);
	}
}

Window class

import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.ButtonGroup;
import javax.swing.JCheckBox;
import java.awt.Font;
import java.awt.event.ItemListener;
import java.awt.event.ItemEvent;
import javax.swing.JLabel;
 
public class groupWindow extends JFrame {
 
	private JLabel testText = new JLabel ("Some writing for test");
 
	private JCheckBox plain;
	private JCheckBox bold;
	private JCheckBox italic;
	private JCheckBox bolditalic;
 
	private Font myFont;
 
	public groupWindow() {
		super("GUI Grouping Test");
		setLayout(new FlowLayout());
 
		// set our default font to plain
		testText.setFont(new Font("Serin", Font.PLAIN, 15));
 
		// make our check boxes
		plain = new JCheckBox("plain", true);
		bold = new JCheckBox("bold", false);
		italic = new JCheckBox("italic", false);
		bolditalic = new JCheckBox("bolditalic", false);
 
		// add the check boxes to the main window
		add(testText);
		add(plain);
		add(bold);
		add(italic);
		add(bolditalic);
 
		// add our check boxes to a group so only one can be selected
		ButtonGroup groupFontAttrib = new ButtonGroup();
		groupFontAttrib.add(plain);
		groupFontAttrib.add(bold);
		groupFontAttrib.add(italic);
		groupFontAttrib.add(bolditalic);
 
		// add a listener to our check boxes
		handler listener = new handler();
		plain.addItemListener(listener);
		bold.addItemListener(listener);
		italic.addItemListener(listener);
		bolditalic.addItemListener(listener);
	}
 
	// create our listener class
	public class handler implements ItemListener {
		public void itemStateChanged(ItemEvent e) {
			// check what box is selected
			if (bolditalic.isSelected())
				myFont = new Font("Serin", Font.BOLD + Font.ITALIC, 15);
			else if (bold.isSelected())
				myFont = new Font("Serin", Font.BOLD, 15);
			else if (italic.isSelected())
				myFont = new Font("Serin", Font.ITALIC, 15);
			else
				myFont = new Font("Serin", Font.PLAIN, 15);
 
			// change our label font now
			testText.setFont(myFont);
		}
	}
}

At the start of the groupWindow it turns yellow and it says "The serializable class groupWindow does not declare a static final serialVersionUID field of type long".

I've been following a tutorial and he hasn't had this issue (it does look like I can suppress this warning but it could be useful to learn).

Thank you in advance,

- Nicky

EDIT:

I'm using Eclipse IDE.

Originally Posted by Norm

Try defining the variable that is mentioned in the message.

I have now and it has gotten rid of the error message...But why, what's the point of that being there? If you're going to say do my own research fair enough, I will eventually learn why

- Nicky

JFrame implements the interface Serializable. All classes that implement this interface need such a variable. Since your class extends JFrame your class does also implement this interface. As such, it needs to implement this variable.
This is not forced upon you, it is not an error if you dont declare this variable, its just a warning.