如何更改 Jpanel 的背景颜色

Question

I have the following code, for a small gui. There is supposed to be a visible Panel at the bottom of the screen but it is never colored when i run the program

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;
import javax.swing.SwingUtilities;

public class GraphPanel extends JPanel implements ActionListener {

private Graphics g;

public void GraphPanel() {
    setOpaque(true);
    setBackground(Color.white);
    this.setBounds(0, 100, 1000, 325);
    this.paintComponent(g);

    setVisible(true);
}
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.setColor(Color.black);
    g.drawLine(40, 120, 40, 300);
}
public void actionPerformed(ActionEvent e) {

}

Have i set this up all correctly?

Answer 1

You are missing a constructor.

Implement a constructor like this:

public GraphPanel(){
     ...
     ...
}

Answer 2

You have a problem in the constructor .

The constructor shall be like below without void :

    public GraphPanel( )
    {
    ...
    }

If you want to add a colored panel in the bottom you could create new JPanel and setBackground(...) add it into the panel you have already with BorderLayout.SOUTH . You should set opaque as well.