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panel with image background and mouse draw

How can I use a image as background in a JPanel if the paint () method is already used for other purposes? (I'm tried to draw over a image in a panel).
Here is my code to draw as a pencil, but I don´t know how to add the image as background ?
#Override
public void paint(Graphics g) {
if (x >= 0 && y >= 0) {
g.setColor(Color.BLACK);
g.fillRect(x, y, 4, 4);
}
}
Thanks Diego

Suggestions:
Don't draw in the JPanel's paint(...) method but rather use it's paintComponent(...) method. There are several reasons for this, one being that if you use the paint(...) method, then you are also responsible for drawing the JPanel's borders and child components and at risk of messing up the rendering of these guys. Also you lose Swing's automatic double buffering.
First call the parent class's super method before calling any other code in the method. This will allow the JPanel to refresh its background and do any graphics housekeeping that may need to be done.
Next draw your background image using g.drawImage(...),
Then do your pencil drawing.

Hovercraft Full Of Eels gave good advice on one direction to take. Here is another.
Display the image in a (ImageIcon in a) JLabel.
When it comes time to paint:
Call createGraphics() on the BufferedImage to gain a Graphics2D object.
paint the lines or other visual elements to the graphics instance.
dispose of the graphics instance.
Call repaint() on the label.
E.G. as seen in this answer.

Drawing images onto AWT and initialising Graphics

I'll start off by telling you what Im trying to do if thats OK, as Im not certain the route Im struggling with is even the best way of achieving my ends.
I have a JFrame containing two JPanels. One contains a number of buttons (buttonPanel), the other is, initially, blank (displayPane). When buttons are pressed the stuff shown in displayPanel changes. The way this is working is each press of a button creates a new object that extends JPanel and then adds that to displayPane
So all the above is working fine and dandy (although I freely admit it may not be the best way of doing it) except for one particular case.
In this particular case I need to create a JLayeredPanel and then draw a clipped image on it. JLayeredPanel because I want to draw some stuff on top of it, clipped because I only want to show part of the area (which exact part is passed to the constructor).
Now, the problem Im having is this. The only way I know to draw a clipped image is through g=thingie.getGraphics(), g.setClip(Shape shape), g.drawImage(various). However, all of that relies on being able to get graphics. But because I am assembling the object first there is no graphics object associated with the JLayeredPane (because its not displayed) so getGraphics is returning null and g.setClip() is throwing a Null Pointer Exception.
Obviously I am doing this wrong somehow and somewhere. Any help would be appreciated, sorry if the question is confusing. I tried to include as much detail as possible and now I am a little concerned I've muddied the issue. I'll keep an eye on this and clarify if required.

Warning!: Wrong answer, see below the line
Why don't you just create a new Graphics object, paint on it and then use it with the update() method?
Graphics g = new Graphics();
g.drawStuff();
thingie.update(g);
This showd be correct
As stated on the comments the previous solution was wrong but it can be done with an Double buffer, create a buffered image and draw on it, then override the paint method of the jLayeredPane pane to draw the image.
private void addStuff() {
BufferedImage bi =
new BufferedImage(100, 100, BufferedImage.TYPE_4BYTE_ABGR);
Graphics bufferedGraphics = bi.getGraphics();
//Paint stuff
bufferedGraphics.drawLine(0, 0, 50, 50);
javax.swing.JLayeredPane layered;
layered = new JLayeredPane() {
#Override
public void paint(Graphics g) {
g.drawImage(bi, 0, 0, null);
}
};
this.add(layered);
this.validate();
this.repaint();
}

Java JPanel on top of JPanel (Drawing on top of drawing)

I am trying to write a code to generate a graph like this: http://www.mathgoodies.com/lessons/graphs/images/line_example1.jpg
I need more than one different line (I hope that's what they are called).
I'm just starting to learn awt and swing. After exhausting three hours of work, I couldn't manage a way to draw a line on top of any other drawing.
I'll try to explain my problem with an example.
Lets say I draw a square like this:
JFrame window = new JFrame();
window.setLayout(null);
window.setVisible(true);
Graph graph = new Graph();
window.add(graph);
//-------------------
public class Graph extends JPanel {
....
public void paintComponent (Graphics g) {
super.paintComponent(g);
g.setColor(Color.white);
g.fillRect(150, 20, x, y);
}
....
}
How do I draw another line or anything else on top of this white square whithout drawing the line in the Graphs paintComponent method? How do I add another JPanel on top of another one, so that both of them are visible? (I'm using JPanel to add some buttons)
Hopefully you can understand what I'm asking.
Thank you!

How do I draw another line or anything else on top of this white square whithout drawing the line in the Graphs paintComponent method?
All custom painting should be done in the paintComponent() method. I'm not sure why you want to add another panel that paints on line. Keep it simple and keep all the painting code in one place.
If you want to add other components (like a JPanel) to the panel then you would use layout managers to lay out the components properly. You would also need to make the components non-opaque by using the setOpaque(...) method.
Another way to layer components is to use a JLayeredPane.
Start by reading the Swing tutorial. There are sections on:
Using Layout Managers
Using Layered Panes.

Drawing text or images on top of gridlayout

I am writing a Tetris-based game, and I am using a GridLayout to display the actual shaft which the Tetris pieces fall down. The GridLayout is filled with little JLabel objects. The shaft is itself a JPanel inside another JPanel, the panel I am using to contain and control the entire game. When the game ends, I want the words "GAME OVER" to appear on top of the grid, possibly accompanied by a small image.
My shaft is an instance of ShaftPanel, which extends JPanel (so that I could override paintComponent) and is a nested private class (so it has access to private instance variables of the larger JPanel). The private instance variable it needs to access is boolean game, which is true when the game is in session and set to false when the game is over. Here is the code for my ShaftPanel class:
public class ShaftPanel extends JPanel {
public ShaftPanel(GridLayout g){
super(g);
}
public void paintComponent(Graphics g){
super.paintComponent(g);
if(game)
return;
g.setColor(Color.WHITE);
g.setFont(new Font("Courier New", Font.BOLD, 15));
char[] c = {'G','A','M','E',' ','O','V','E','R'};
g.drawChars(c,0,c.length,45,45);
}
}
I have one method in the larger class calling the repaint() method of shaft at the appropriate time. Adding a print statement indicates that the paintComponent method is being called when I want it to, and the setColor, setFont, drawChars methods are all being called at the correct times. However, nothing shows up. I highly suspect that the text is being drawn underneath the grid of JLabels, so that it can't be seen, but I don't know how to fix this problem. The JLabels inside the grid have to stay opaque, because the program relies on them being different colors. Is there a way to tell paintComponent to draw the text on top of anything else in the panel?

See the section from the Swing tutorial on Using a Glass Pane for an example and explanation on how a glass pane works.
Another option is to use a JWindow to display a label with your message and icon.

I would probably not have made tetris this way, but one way to test this would be to remove the "if(game)" and see if game over is being written even when no JLabels are there (unless they are always there and sometimes are blank).
At any rate, I think what might be useful though I don't think I have ever used it is a GlassPanel.... This is a panel that can be overlayed on your current JFrame etx...
Look Here for more code and info: http://www.java2s.com/Code/Java/Swing-JFC/Paintonglasspane.htm

Adding a watermark to a JTextArea

Is they a way of adding a watermark to a JTextArea?

I suspect that you'd need to subclass JTextArea and override the paintComponent() method, drawing your background image first and calling super.paintComponent() to render the text:
public void paintComponent (Graphics g) {
g.drawImage(watermark, 0, 0, this);
super.paintComponent(g);
}
edit: as pointed out by camickr, a JTextArea is opaque, so your subclass will need to change this by calling setOpaque(false).

I doubt the suggestion given above will work. A JTextArea is opaque, so the text will paint over top of the image. So at the very least you will need to make the text area non-opague and you will then need to play with the background colors of the viewport and/or scrollpane.
If you want a reusable solution try creating an ImageBorder. The order of painting is:
a) paintComponent
b) paintBorder
c) paintChildren
So if you add the border to the text area it will paint on top of the text in a fixed location.
Or if you add the border to the viewport it will paint below the text is a floating location.

You may also consider using JXLayer which can create quite complex visual effects