Canvas and MouseListener...

**fkmk** · June 2nd, 2014, 07:13 PM

Look: I press the button e.g Pencil and I draw something on my JPanel. After that, I want to sketch in something on JPanel by brush, so I press the button, which calls Action of Paintbrush. I draw something, and I note that, the older "picture" disappear. It is replaced by new "picture". When I press Pencil button again, latest picture is replaced by new one, and so on.

Something like that.

Sorry for my English in advance. :}

**Norm** · June 2nd, 2014, 07:51 PM

Use a collection like an ArrayList to save the points used to make the drawing.
Then save that list in another list.
That way all the previous drawings will be saved and can be retrieved by going through the list getting the lists it contains to draw the older pictures.

**fkmk** · June 3rd, 2014, 03:54 PM

Norm, should I have to create ArrayList of ArrayList in Drawing class? I have no idea, how to "include" there Arrays from e.g Pencil class (which include drawn points).
Thanks

edit//
I have a problem with NullPointerException. I am looking for an error for two days, and I can not find where is the problem...

Here is the class:

public class Lines extends Tool {
 
	private int x, y;
	private final ArrayList<Point[]> pointsList = new ArrayList<>();
	private final ArrayList<Color> Colors = new ArrayList<>();
	private Drawing drawingArea;
        private Point[] points = new Point[2];
 
	public Lines() {}
	public Lines(Drawing drawingArea) {
			System.out.println("LINES SELECTED!"); 
			this.drawingArea = drawingArea;
	}
 
	// ================================================================= //
 
	@Override
	public void paintComponent(Graphics g) {
		((Graphics2D) g).setStroke(new BasicStroke(2));
            for (Point[] Points : pointsList) {
                Point p1 = Points[0];
                Point p2 = Points[1];
                g.drawLine(p1.x, p1.y, p2.x, p2.y);
            }
	}
 
	// ================================================================= //
 
	@Override
	public void mousePressed(MouseEvent e) {
        points[0] = null;
        points[1] = null;
            pointsList.add(points);
		Colors.add(GUI.getColour());
		x = e.getX();
	    y = e.getY();
        pointsList.get(pointsList.size()-1)[0] = new Point(x, y);
	}
 
	@Override
	public void mouseDragged(MouseEvent e) {
		x = e.getX();
        y = e.getY();
        pointsList.get(pointsList.size()-1)[1] = new Point(x, y);
		drawingArea.repaint();
	}
 
	@Override
	public void mouseReleased(MouseEvent e) {
		x = e.getX();
        y = e.getY();
        pointsList.get(pointsList.size()-1)[1] = new Point(x, y);
		drawingArea.repaint();
	}
 
	@Override
	public void mouseMoved(MouseEvent e) {}
	@Override
	public void mouseClicked(MouseEvent e) {
 
	}
	@Override
	public void mouseEntered(MouseEvent e) {}
	@Override
	public void mouseExited(MouseEvent e) {}
}

and compiler says:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at Toolkit.Lines.paintComponent(Lines.java:39)
	at GUI.Drawing.paintComponent(Drawing.java:43)
	at javax.swing.JComponent.paint(JComponent.java:1053)
	at javax.swing.JComponent.paintToOffscreen(JComponent.java:5217)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1532)
	at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1455)
	at javax.swing.RepaintManager.paint(RepaintManager.java:1252)
	at javax.swing.JComponent._paintImmediately(JComponent.java:5165)
	at javax.swing.JComponent.paintImmediately(JComponent.java:4976)
	at javax.swing.RepaintManager$3.run(RepaintManager.java:811)
	at javax.swing.RepaintManager$3.run(RepaintManager.java:794)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:794)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
	at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
	at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
	at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1680)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:744)
	at java.awt.EventQueue.access$400(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:697)
	at java.awt.EventQueue$3.run(EventQueue.java:691)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:714)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

edit:// I noted, that Points[1] is null, but I don't know why...

**Norm** · June 3rd, 2014, 04:00 PM

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Toolkit.Lines.paintComponent(Lines.java:39)

What variable on line 39 has a null value when that line is executed?

**fkmk** · June 3rd, 2014, 04:12 PM

Norm, debugger said, that

                Point p2 = Points[1];
                g.drawLine(p1.x, p1.y, p2.x, p2.y);

there is null.

**Norm** · June 3rd, 2014, 04:22 PM

You posted two lines. Which one is line 39? What variable on line 39 had a null value?

**fkmk** · June 3rd, 2014, 04:27 PM

Norm, it is line 39:

                g.drawLine(p1.x, p1.y, p2.x, p2.y);

Point p2 and Points[1] had a null value.

**Norm** · June 3rd, 2014, 04:32 PM

p2 and Points[1] had a null value

The next question is: why does Points[1] have a null value?

What is in pointsList? Print its contents to see.

**fkmk** · June 3rd, 2014, 05:11 PM

Norm, I don't know why Points[1] have a null value... :/ in my opinion it should iclude any value.
pointsList is a list with all points which mouse intercepted.

**Norm** · June 3rd, 2014, 05:23 PM

What is in pointsList? Print its contents to see.
You are hoping it will have something in it. What is there?

**fkmk** · June 3rd, 2014, 05:51 PM

Norm, ok, I printed a content with this code:

		for(Point[] array: pointsList) {
			System.out.println(array);
		}

and in the console it printed:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at Toolkit.Lines.paintComponent(Lines.java:40)
	at GUI.Drawing.paintComponent(Drawing.java:45)
	at javax.swing.JComponent.paint(Unknown Source)
	at javax.swing.JComponent.paintToOffscreen(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
	at javax.swing.RepaintManager.paint(Unknown Source)
	at javax.swing.JComponent._paintImmediately(Unknown Source)
	at javax.swing.JComponent.paintImmediately(Unknown Source)
	at javax.swing.RepaintManager$3.run(Unknown Source)
	at javax.swing.RepaintManager$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.access$1100(Unknown Source)
	at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
	at java.awt.event.InvocationEvent.dispatch(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$400(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)
[Ljava.awt.Point;@72efb4de
[Ljava.awt.Point;@63449552
[Ljava.awt.Point;@7acd519e
[Ljava.awt.Point;@4f564b40
[Ljava.awt.Point;@1cb6b662
[Ljava.awt.Point;@14c579b0

**Norm** · June 3rd, 2014, 05:54 PM

Try printing pointsList BEFORE accessing it.

**fkmk** · June 3rd, 2014, 05:59 PM

Norm, it prints only one point

[Ljava.awt.Point;@3ff8bf54

It is what it prints after one drawing with mouse.

I don't know, if I understand what you mean, but printing before accessing shows nothing, empty field.

**Norm** · June 3rd, 2014, 06:08 PM

Please post the code that defines pointsList and the print statement that printed what was posted in post#63.

The print out in post#63 is for a Point array, not the contents of an ArrayList.

**fkmk** · June 3rd, 2014, 06:18 PM

Norm, here is the code that defines pointsList:

	private final ArrayList<Point[]> pointsList = new ArrayList<>();

and the code with the print statement:

		for(Point[] array: pointsList) {
			System.out.println(array);
		}

I don't know if it is what you ment, but I hope so.

**Norm** · June 3rd, 2014, 06:27 PM

When you print pointsList, I'd expect to see something like this:
[[Ljava.awt.Point;@5df3c5]

Note [[ in front and ] at the end.

What you have printed is the first item in pointsList, NOT the whole thing like the following:
System.out.println("pointsList="+pointsList);

Change your code to this:

  for(Point[] array: pointsList) {
	System.out.println(java.util.Arrays.toString(array));
  }

to print out the contents of the Point array.

**fkmk** · June 3rd, 2014, 06:34 PM

Norm, oh, sorry for that...

Here is what shows in console:

[java.awt.Point[x=400,y=219], java.awt.Point[x=404,y=219]]

Printing before accessing shows nothing, empty field.

**Norm** · June 3rd, 2014, 06:37 PM

Nothing null there. That looks like good values.
Where is the null value coming from?

Is that being printed in the paintComponent() method just before the statement where the exception happens?

**fkmk** · June 3rd, 2014, 06:59 PM

Norm, sorry, I cut something.
Here is the full code:

[java.awt.Point[x=286,y=371], null]
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at Toolkit.Lines.paintComponent(Lines.java:43)
	at GUI.Drawing.paintComponent(Drawing.java:45)
	at javax.swing.JComponent.paint(Unknown Source)
	at javax.swing.JComponent.paintToOffscreen(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
	at javax.swing.RepaintManager.paint(Unknown Source)
	at javax.swing.JComponent._paintImmediately(Unknown Source)
	at javax.swing.JComponent.paintImmediately(Unknown Source)
	at javax.swing.RepaintManager$3.run(Unknown Source)
	at javax.swing.RepaintManager$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.access$1100(Unknown Source)
	at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
	at java.awt.event.InvocationEvent.dispatch(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$400(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)
[java.awt.Point[x=286,y=371], java.awt.Point[x=289,y=369]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=297,y=365]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=310,y=362]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=322,y=358]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=336,y=354]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=348,y=351]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=358,y=346]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=366,y=342]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=373,y=338]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=378,y=335]]
[java.awt.Point[x=286,y=371], java.awt.Point[x=380,y=333]]

I'm so sorry for my weird responses, its very late.

**Norm** · June 3rd, 2014, 07:05 PM

[java.awt.Point[x=286,y=371], null]

That shows that the second point in the array is null. Why doesn't it have a valid value?
Either make sure it has a valid value before it is used
or test for a null value and don't use it

**fkmk** · June 3rd, 2014, 07:07 PM

Norm, yes, Points[1] is null... but I don't know why. My code looks ok and I don't see any mistakes in it.

**Norm** · June 3rd, 2014, 07:14 PM

Where is the value set? Why does the code use it before it is given a value?
Add some println statements to show when the code that sets it is executed and when the paintComponent() method is called. That should show you the order that the code is executed.

Add a test in the code to not use it if it is null.

**fkmk** · June 3rd, 2014, 07:23 PM

Norm, I added test, as you said and it works! Thank you again! Let God bless you!

Thank you for all your help! If you will have any problems with everything, ask me, and I will help you also!
Thanks again!

**Norm** · June 3rd, 2014, 07:25 PM

Glad you have it working. You might still want to see why the second point doesn't have a value when the paintComponent() method is called.

**fkmk** · June 3rd, 2014, 07:32 PM

Norm, yes, I'm curious about it, but I still have no idea, why it happened. :/

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