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Java 2D Graphics BufferedImage FillRect issue

I am still getting used to painting graphics on java and am trying to write a simple graphics program that paints a background using a buffered image. However, strangely enough, even though my jpanel size is set to 1200x400 and so are the buffered image and fillrect method, there is a small "gap" as you can see in the picture I have attached so the panel is clearly larger than 1200x400 but I don't understand why? What does the setPreferredSize method actually do? Also when I change my fillrect method and bufferedimage to 1300x500 there is no longer a gap so this is clearly the issue. If anyone has any advice as to where I am going wrong I would greatly appreciate it, thanks
Here is my code:
public class Q2 extends JPanel {
private BufferedImage image;
public static void main(String[] args) {
Q2 test = new Q2();
}
public Q2() {
this.init();
}
private void init() {
JFrame window = new JFrame();
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setContentPane(this);
this.setPreferredSize(new Dimension(1200,400));
refreshCanvas();
window.pack();
window.setVisible(true);
window.setResizable(false);
}
public void paintComponent(Graphics g) {
Graphics2D twoD = (Graphics2D) g;
twoD.drawImage(image,0,0,null);
}
private void refreshCanvas() {
image = new BufferedImage(1200,400,BufferedImage.TYPE_INT_ARGB);
Graphics2D twoD = image.createGraphics();
twoD.setColor(Color.BLACK);
twoD.fillRect(0, 0, 1200,400);
repaint();
}
}

Have a look at this answer here.
You have to put window.setResizeable(false); before window.pack();. This should fix it.

Panel doesn't have border

I'm working on a project and I just started on the GUI. Since this isn't my most favorite topic, I stumbled real quick on something not working quite right. Everything (PacmanGrid,PacmanScore) is shown correctly but the borders I wrote for the PacmanScore Panel! Anyway here is the code, hope someone can help.
public class PacmanFrame extends JFrame{
public PacmanFrame() {
this.setLayout(new BorderLayout());
this.setTitle("Pacman");
PacmanGrid p1=new PacmanGrid();
PacmanScore p2 = new PacmanScore();
this.add(p1,BorderLayout.CENTER);
this.add(p2,BorderLayout.EAST);
super.setDefaultCloseOperation(EXIT_ON_CLOSE);
super.repaint();
pack();
super.setVisible(true);
}
public static void main(String[] args) {
PacmanFrame p1 = new PacmanFrame();
}
}
PacmanScore
public class PacmanScore extends JPanel{
private TitledBorder t3 = BorderFactory.createTitledBorder("Menu");
private Border etched = BorderFactory.createEtchedBorder(Color.WHITE, Color.white);
public PacmanScore() {
setLayout(new FlowLayout());
setPreferredSize(new Dimension(100,800));
setBackground(Color.DARK_GRAY);
t3.setBorder(etched);
setBorder(t3);
setVisible(true);
setOpaque(true);
}
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D)g;
super.paintComponent(g2);
g2.setColor(Color.white);
g2.drawString("Score: ", 20, 400);
}
}
PacmanGrid is also extended by a Panel and draws the classical PacmanGrid using predefined patterns. But I don't think it is relevant since the problem is clearly on the PacmanScore Panel. I will post the code if anyone needs tho.
Thanks in Advance!

public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D)g;
super.paintComponent(g2);
g2.setColor(Color.white);
g2.drawString("Score: ", 20, 400);
}
You didn't override paint() properly because you didn't invoke super.paint() and therefore the border is not painted.
Don't override paint(). Custom painting is done by overriding paintComponent().
Read the section from the Swing tutorial on A Closer Look at the Paint Mechanism for more information.
Why are you even doing custom painting? Just add a JLabel to the panel.
Also, Swing components (except for top level windows) are visible by default so there is no need to make the panel visible.

Getting wrong output in adding an image in JFrame

My problem is that when I create or draw an image in JFrame by using
public void paint(Graphics g)
{}
Method I am getting a black screen instead of the image the problem code snippet is
ImageIcon i=new ImageIcon("logo.png);
Image im=i.getImage();
public void paint(Graphics g)
{
g=getGraphics();
}
Please suggest me an alternative method or solution to my problem
Thanks in advance

Would you consider using a JPanel and overriding the paintComponent method? Something like this:
BufferedImage image = ... //i'll leave this blank since there are several ways to get a bufferedimage. I'll leave an eg: ImageIO.read(new File("/path/to/image"));
JPanel pane = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(image, 0, 0, null);
}};
and then adding the panel to your frame. You can do the same with the container in the JFrame. The logic is simillar.

Having images as background of JPanel

I am new in Java and I am currently creating a game with graphics. I have this class that extends from JFrame. In this class, I have many JPanels that needs an image as background. As I know, to be able to paint images in the JPanel, I need to have a separate class that extends from JPanel and that class's paintComponent method will do the work. But I don't want to make separate classes for each JPanel, I have too many of them; and with the fact that I am only concerned with the background. How can I do this? is it with an anonymous inner class? How?
For better understanding I provided some code:
public GUI extends JFrame {
private JPanel x;
...
public GUI() {
x = new JPanel();
// put an image background to x
}

Why not make a single class that takes a Image??
public class ImagePane extends JPanel {
private Image image;
public ImagePane(Image image) {
this.image = image;
}
#Override
public Dimension getPreferredSize() {
return image == null ? new Dimension(0, 0) : new Dimension(image.getWidth(this), image.getHeight(this));
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.drawImage(image, 0, 0, this);
g2d.dispose();
}
}
You would even provide hints about where it should be painted.
This way, you could simply create an instance when ever you needed it
Updated
The other question is, why?
You could just use a JLabel which will paint the icon for you without any additional work...
See How to use labels for more details...
This is actually a bad idea, as JLabel does NOT use it's child components when calculating it's preferred size, it only uses the size of the image and the text properties when determining it's preferred size, this can result in the component been sized incorrectly

You don't have to make another class for it? You could just do:
x = new JPanel(){
public void paintComponent(Graphics g){
super.paintComponent(g);
//draw background image
}
};

You can do this in single line:
panelInstance.add(new JLabel(new ImageIcon(ImageIO.read(new File("Image URL")))));
I hope it will work for you.

image resize to fit on JPanel

I have JPanel Which will load images.
Since images will not have the same width and height as the JPanel, I want to make the image resize and fit in the JPanel.

Read on this article, The Perils of Image.getScaledInstance()
Now IF you STILL prefer you can use something like,
Image scaledImage = originalImage.getScaledInstance(jPanel.getWidth(),jPanel.getHeight(),Image.SCALE_SMOOTH);
this before loading the image to your JPanel, probably like discussed in this answer.

I know this is quite old, but maybe this helps other people
use this class instead of a normal JLabel and pass an ImageIcon when using setIcon(#);
private class ImageLabel extends JLabel{
private Image _myimage;
public ImageLabel(String text){
super(text);
}
public void setIcon(Icon icon) {
super.setIcon(icon);
if (icon instanceof ImageIcon)
{
_myimage = ((ImageIcon) icon).getImage();
}
}
#Override
public void paint(Graphics g){
g.drawImage(_myimage, 0, 0, this.getWidth(), this.getHeight(), null);
}
}