JFrame not updating with Background change

Question

I created a class were bosex are displayed, and it reads where you click, and the handler changes the background color based on the location of you click, Everything works except for the updating of the JFrame. I tried 3 different lines of code, as shown in the handler. Code:

public class Dynamic_Bg_Color extends JFrame{

private static final long serialVersionUID = 1L;

JFrame frame;

Handler handler = new Handler();

static Dimension size = new Dimension(500,400);

public Dynamic_Bg_Color(){


    frame = new JFrame("BG Color Changer");

    frame = this;

    setBackground(Color.cyan);

    frame.addMouseListener(handler);

}

public void paint(Graphics g1){

    System.out.println("Click");

    Graphics g = (Graphics)g1;

    g.setColor(Color.blue);
    g.fillRect(20,20,frame.getWidth()-40,100);

    g.setColor(Color.green);
    g.fillRect(20,140,frame.getWidth()-40,100);

    g.setColor(Color.orange);
    g.fillRect(20,260,frame.getWidth()-40,100);
}

public static void main(String[] args){

    Dynamic_Bg_Color d = new Dynamic_Bg_Color();

    d.frame.setPreferredSize(new Dimension(size));
    d.frame.setMinimumSize(new Dimension(size));
    d.frame.setMaximumSize(new Dimension(size));
    d.frame.setLocationRelativeTo(null);

    d.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    d.frame.setLayout(new FlowLayout());
    d.frame.setVisible(true);
}

public class Handler implements MouseListener{

    public void mouseClicked(MouseEvent e) {

    }
    public void mousePressed(MouseEvent e) {

        int x = e.getX();
        int y = e.getY();

        if(x>= 20 && x<=frame.getWidth()-40 && y>=20 && y<= 120){
            setBackground(Color.blue);
        }
        if(x>= 20 && x<=frame.getWidth()-40 && y>=140 && y<= 240){
            getContentPane().setBackground(Color.green);
        }
        if(x>= 20 && x<=frame.getWidth()-40 && y>=260 && y<= 360){
            frame.getContentPane().setBackground(Color.orange);
        }
        repaint();
    }

//Implemented Methods, cut to shorten, no code in them//

}

}

Answer 1

1. Don't override paint of top level containers. They are responsible for maintaining a complex paint chain (which you have now broken) and they aren't double buffered which can result in flickering when painted.
2. Do call super.paintXxx.

Instead of extending JFrame, use JPanel. Instead of overriding paint, override paintComponent. Call super.paintComponent before you do any other custom painting. It is responsible for painting the background

Finally, add this panel to a instance of JFrame...

Take a look at Performing Custom Painting for more details

Updated with runnable example

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Dynamic_Bg_Color extends JPanel {

    private static final long serialVersionUID = 1L;

    public Dynamic_Bg_Color() {
        setBackground(Color.cyan);
        addMouseListener(new Handler());
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(500, 500);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        System.out.println("Click");

        g.setColor(Color.blue);
        g.fillRect(20, 20, getWidth() - 40, 100);

        g.setColor(Color.green);
        g.fillRect(20, 140, getWidth() - 40, 100);

        g.setColor(Color.orange);
        g.fillRect(20, 260, getWidth() - 40, 100);
    }

    public class Handler extends MouseAdapter {

        @Override
        public void mousePressed(MouseEvent e) {

            int x = e.getX();
            int y = e.getY();

            System.out.println(x + "x" + y);

            if (x >= 20 && x <= getWidth() - 40 && y >= 20 && y <= 120) {
                setBackground(Color.blue);
            }
            if (x >= 20 && x <= getWidth() - 40 && y >= 140 && y <= 240) {
                setBackground(Color.green);
            }
            if (x >= 20 && x <= getWidth() - 40 && y >= 260 && y <= 360) {
                setBackground(Color.orange);
            }
            repaint();
        }

    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                Dynamic_Bg_Color d = new Dynamic_Bg_Color();

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(d);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

}