Image on JPanel ---> Canvas

[justyStepi]

Hello,

I'm trying to add an Image to my JPanel, but I'm not sure how to add it. I know there are lots of thread like this available, but for me I can't get it working.

I found that for adding picture I can use Canvas. Can you pls help me and show me what I'm doing wrong?

here is the code ....

		Maps = new JPanel();
		mainTab.addTab("Maps", null, Maps, null);
 
		Gcanava canvas = new Gcanava();
		Maps.add(canvas);

Here the mainTab is a JTabbledPanel and I have a Maps panel on it.

Gcanava is different class where I have the code for adding picture:

class Gcanava extends JComponent{
	/**
	 * 
	 */
 
	public void paint(Graphics g){
//		Graphics2D g2 = (Graphics2D) g;
//		
//		Image img = Toolkit.getDefaultToolkit().getImage("pictures/map.jpg");
//		g2.drawImage(img, 100, 100,this);
//		g2.finalize();

Can you please help me.

Thanks

[Norm]

You should override the paintComponent() method in Swing classes not paint().
Load the image one time outside of the paintComponent method, not every time the method is called.

Give the component a size (setPreferredSize) or it could have a size of 0

[justyStepi]

hey,

I change the paint() to paint Component()
[/CODE]
Image img;
Graphics g;

public void paintComponent(Graphics g){

}
public Gcanava(){
try{

img =ImageIO.read(new File("pictures/map.jpg"));

}
catch(IOException e){
g.drawImage(img,0,0,this);
}


}

}
[/CODE]

Where should I change the size? of the Graphics g? or the Image?

And also now, when I do it, the whole JPanel turns into canvas which I dont want to I want to have a some other components there.

How can i do that

[Norm]

Set the size of the Gcanava object. The container's layout manager will use that size when it positions the object.

[justyStepi]

I kinda changed it, but now im having problems with these exceptions,why?


at Gcanava.<init>(Gcanava.java:33)
at NewExample.initialize(NewExample.java:343)
at NewExample.<init>(NewExample.java:78)
at NewExample$1.run(NewExample.java:65)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectio nPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(U nknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

[Norm]

You left off the first lines of the error message that say what the exception was.

[justyStepi]

It was : java.lang.NullPointerException :/

[Norm]

Look at line 33 and find the variable that has the null value and then backtrack in the code to find out why the variable does not have a valid non-null value.

[justyStepi]

Well , line 33 is ---> g.drawImage(img,200,200,this); it used to be set to 0 and 0 but I changed it to 200. And I thought that it will help but it doesnt,why?

[Norm]

what variable has the null value? 200 vs 0 would not cause an exception.

[justyStepi]

I just found that it might be because of the size of the image. The image might be bigger then my frame size. And for this reason I might be having troubles. Is it possible?

[Norm]

I don't think that will cause a null pointer exception.

[justyStepi]

Hmm...I can provide you the whole code if you want nd you can see whats happening..

[Norm]

You should be able to find what variable is null. Add a println just before where the error occurs and print out the variables that are on the line with the error. The print out will show you which variable is null.

[justyStepi]

Console says that it's the line 33 which is the g.drawImage(img,200,200,this); but it's kinda weird. how this can give me an nullPointerException when the dimension is given

[Norm]

did you print out the variables? what was null?

[justyStepi]

Wtf!!

Right now I commented out thise part of the code nd use [/CODE]
class Gcanava extends JComponent{
/**
*
*/
Image img;
Graphics g;

public void paintComponent(Graphics g){
Graphics2D g2 = (Graphics2D) g;

Image img = Toolkit.getDefaultToolkit().getImage("images/map.jpg");
g2.drawImage(img, 100, 100,this);
g2.finalize();

}


public Gcanava(){
// try{
//
// img =ImageIO.read(new File("images/map.jpg"));
//
// }
// catch(IOException e){
// g.drawImage(img,200,200,this);
// }
//

}

}
[/CODE]

nd I run it, no exception at all, and even a "border" for the picture appeared on my JPanel why??

[Norm]

What variable was null?

[justyStepi]

Maybe g? I dont know, since the line 33 g.drawImage(); is commented out

[Norm]

A commented out line would not cause an exception.