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Drawing to a buffered image inside a Jpanel

i am currently trying to make a canvas that i can draw stuff to and have it appear inside a JFrame.
To do this, i intend to have a BufferedImage inside a JPanel component that the paintComponent method can draw from.
Ideally from the given JFrame i want to be able to reference this buffered image, and then draw stuff to it using its Graphics2D that the paintComponent method can then show when it draws using the buffered image.
I'm doing this to avoid using the paintcomponent method directly, i want to be able to reference this canvas from anywhere in the program and have it be painted when the frames repaint() method is called.
class MyPanel extends JPanel {
BufferedImage img = new BufferedImage(500, 500, BufferedImage.TYPE_INT_ARGB);
Graphics2D imgG2 = img.createGraphics();
public Graphics2D getGraphics() {
return imgG2;
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
int w = img.getWidth();
int h = img.getHeight();
g2.drawImage(img, 0, 0, w, h, null);
}
}
class Main {
private static JFrame createAndShowGui() {
JFrame frame = new JFrame("droneFrame");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.add(new MyPanel());
frame.setSize(500, 500);
frame.setResizable(false);
frame.setVisible(true);
return frame;
}
public static void main(String args[]) {
JFrame frame = createAndShowGui();
//Something here to reference the inner Jpanels imgG2 field, and draw to it.
frame.repaint();
//Draw whatever is currently in the buffered image.
}
}
However, i'm at a loss at how to do this, since frame.getComponent(0) just returns a Component, rather than the specfic type of component it is.
Thanks in advance.

Just managed to figure this out, you need to set the content pane of your JFrame to the JPanel, then to reference the graphics of the buffered image, you need to get the content pane of the JFrame, and downcast it to the specific type MyPanel.
Now you have the content pane in the correct format, and can reference the graphics since it now has that field.

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.

draw buffered image ontop of another buffered image

my goal is to draw some bufferedimage onto another. then all this stuff draw onto some other bufferedimage and so on. And finally draw this on top of a panel.
For now i'm trying to draw bufferedimage onto panel and nothing works. My bufferedimage looks completely white:
public class Main2 {
public static void main(String[] args) {
JFrame frame = new JFrame("asdf");
final JPanel panel = (JPanel) frame.getContentPane();
frame.setSize(500,500);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
panel.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
somepaint(panel);
}
});
}
private static void somepaint(JPanel panel) {
BufferedImage image = new BufferedImage(200,200,BufferedImage.TYPE_INT_ARGB);
image.getGraphics().setColor(Color.red);
image.getGraphics().fillRect(0, 0, 200, 200);
Graphics2D graphics = (Graphics2D) panel.getGraphics();
graphics.setColor(Color.magenta);
graphics.fillRect(0, 0, 500, 500);
graphics.drawImage(image, null, 0, 0); // draws white square instead of red one
}
}
thanks

Re:
private static void somepaint(JPanel panel) {
BufferedImage image = new BufferedImage(200,200,BufferedImage.TYPE_INT_ARGB);
image.getGraphics().setColor(Color.red);
image.getGraphics().fillRect(0, 0, 200, 200);
Graphics2D graphics = (Graphics2D) panel.getGraphics();
This is not how you draw inside of a JPanel or JComponent.
Don't call getGraphics() on a component as the Graphics object returned will be short-lived, and anything drawn with it will not persist. Instead do your JPanel's drawing inside of its paintComponent(Graphics G) method override. You will need to create a class that extends JPanel in order to override paintComponent(...).
Most importantly, to see how to do Swing graphics correctly, don't guess. You'll want to read the Swing Graphics Tutorials first as it will require you to toss out some incorrect assumptions (I know that this is what I had to do to get it right).

You need to rectify your parameters in the drawImage() call. Change this:
graphics.drawImage(image, null, 0, 0);
to
graphics.drawImage(image, 0, 0,null);
Check the Java docs for more details.

JFrame image display at frame resize

I have this JFrame containing a children of JPanel wherein it displays the image which is declared in this manner.
BufferedImage image = ImageIO.read(filename);
The program displays the image properly. But the only thing is, it requires to resize the frame to display the image.
Is there a possible way to display the image once the frame appears?

You should override paintComponent(Graphics g) and draw the image therein. In this case, you should do this for the JPanel component (I think? If not, do this for the JComponent(s) you're referring to). Also, since Swing is not thread-safe, ensure these modifications are performed in the EDT.
EXAMPLE
public class Demo{
private static BufferedImage bi;
public static void main(String[] args){
try{
loadImage();
SwingUtilities.invokeLater(new Runnable(){
#Override
public void run(){
createAndShowGUI();
}
});
}
catch (IOException e){
// handle exception
}
}
private static void loadImage() throws IOException{
bi = ImageIO.read(new File("src/resource/braveheart.PNG"));
}
private static void createAndShowGUI(){
final JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final JPanel panel = new JPanel(){
#Override
protected void paintComponent(Graphics g){
Graphics g2 = g.create();
g2.drawImage(bi, 0, 0, getWidth(), getHeight(), null);
g2.dispose();
}
#Override
public Dimension getPreferredSize(){
return new Dimension(bi.getWidth(), bi.getHeight());
}
};
frame.add(panel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
OUTPUT
It's important to keep in mind that this example ignores rendering hints, so when you maximize the JFrame, the image quality will be very poor. :)
EDIT
When answering this question, I assumed you had a basic understanding of Swing. I suppose I assumed too much. It is important to mention that all components should be added to the top-level container before it's been realized (i.e. made visible). This will ensure that everything is rendered without having to resize your frame. As others have suggested, you could have simply used a JLabel to render the image, and then added it to your JPanel. Instead, I promoted custom painting, which is perfectly acceptable, and to me, cleaner.

for dispaly Image or ImageIcon is better look for JLabel (basic stuff)

Why won't this render?

here is my code:
import java.awt.*;
class g
{
public static void main(String arg[])
{
System.out.println("hello");
Rectangle rec=new Rectangle(4,4);
Graphics2D.draw(rec);
}
}
when i try to compile it i get this:
non-static method draw(java.awt.Shape) cannot be referenced from a static context
this confuses me. Why does this happen? If Graphics2D is an abstract Class how can Graphics2D.draw(shape s) be non-static?

If Graphics2D.draw was static, where would you expect the rectangle to be drawn? The top, left corner of your monitor? The currently active window? Inside a new window?
Graphics2D.draw is not static because there are many graphics contexts in which you could be drawing. Explain to us where you expect the rectangle to be drawn and we can help you obtain the appropriate Graphics2D object to suit your needs.
If you want to learn about graphics, you should be able to do something like this:
public class MyGraphicsFun {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setSize(800, 600);
frame.add(
new JComponent() {
public Dimension getPreferredSize() {
return new Dimension(800, 600);
}
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.RED);
// Any other drawing you want...
}
}
);
frame.setVisible(true);
}
}
Disclaimer: This code was written from memory, so it could have errors

Not in this javadocs:
http://download.oracle.com/javase/6/docs/api/
Which one are you looking at?
Besides, why don't you believe the compiler? What's the point of disagreeing if you'll never get it past the compiler? Just do what it says and get on with it.
You sound like a lost soul. Start with this:
http://download.oracle.com/javase/tutorial/2d/index.html