Question

I’m trying to extend a class to eventually make a custom button. I read in several places that it’s best to extend as high as possible on the heirarchy (for better polymorphism?), so I’m trying to extend JComponent:

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

public class TestButton extends JComponent {
    private static final long serialVersionUID = 1L;
    
    
    public TestButton() {
        super();        
    }
    
}

And the code that calls this is:

 b1 = new TestButton();     
 basePanel.add(b1,gbc);  // (gbc is GridBagConstraints object)

The thing is, my JComponent isn’t displayed in my layout. If I extend the class as JButton, it shows no problem. What’s the deal?

Update:

FYI, this is sort of a noob conceptual question, I’m far from proficient here obviously.

Here’s a picture to describe. The only thing changed is extends ______.

What should be happening is a purple-filled block, the same height as the yellow block on the bottom.

What is happening is a default sized block that has no background (the black is from the JFrame).

Answer 1

It is a blank component (basically a template). It has no properties. You have to add your own graphical elements by overriding the paintComponent method and then add logical elements by overriding the update method.