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Clearing Graphics from an outer class method

So I have a college project to make paint program using swing , I need to clear Graphics object and but from a method in an outside class and then draw all shapes again (refreshing the graphics object) as I'm passing the graphics object through this method .
the class is responsible for saving all shapes i draw on this graphics (in an ArrayList ) .
SO how can I do this if I can't call Super.paintComponent that exists in the Jpanel class .

as I'm passing the graphics object through this method .
You should NOT be passing the Graphics object. The paintComponent() method (or any method is invokes) should always use the Graphics object passed to the paintComponent() method.
SO how can I do this if I can't call Super.paintComponent that exists in the Jpanel class .
In the class where you do the custom painting you create a clear() method. This will simply remove all the Shape objects from the ArrayList and then invoke repaint().
See the DrawOnComponent example from Custom Painting Approaches that demonstrates how this is done.

Found a very simple answer which is "Draw white rectangle, then draw shapes again"
that would simply solve my problem :)

What is the JPanel/Graphics method paintComponent?

So I'm trying to learn Java graphics and this bit of code has me perplexed. I don't understand a couple things here:
Why is paintComponenet used twice for the name of the method and as
we call a method from super (JPanel)?
What is Graphics g, isn't it just a reference variable for an object
of Graphics since we don't set it equal to = new Graphics();?
Why does the method name in my class have to be paintComponent to
call upon the method paintComponent from JPanel or super?
The method in my class paintComponent takes the parameter of a
Graphics object but when does paintComponent even get called and
when is the parameter of Graphics inserted?
Essentially I need someone to explain this code to me.
//note this is all in a class that extends JPanel, my JPanel is later placed in
//a JFrame which is run through main
public void paintComponent(Graphics g)
{
int width = getWidth();
int height = getHeight();
super.paintComponent(g);
g.setColor(Color.RED);
g.fillRect(10, 10, 200, 200);
g.setColor(Color.BLUE);
g.drawRect(10, 10, 200, 200);
}

Why is paintComponenet used twice, for the name of the method and as we call a method from super (JPannel)
It's not "used" twice. It is overridden once, but you want to call the parent (JPanel) class's super method so that you're sure that it does its own house-keeping painting, including painting its children and clearing out any dirty bits from the screen.
What is Graphics g, isn't it just a reference variable for an object of Graphics since we don't set it equal to = new Graphics();
It's a Graphics parameter. You don't set it = new Graphics() because the JVM does this for you. It calls the method behind the scenes when needed, and provides the parameter.
Why does the method name in my class have to be paintComponent to call upon the method paintComponent from JPannel or super
It has to override the super's method so that the JVM calls the right method when it wants to draw the GUI.
The method in my class paintComponent takes the parameter of a Graphics object but when does paintComponent even get called and when is the parameter of Graphics inserted.
Again, it is called by the JVM when either your program wants to repaint the GUI, such as when you call repaint() or when the operating system wants to repaint a window such as if a window is minimized and restored.
You really really want to read the graphics tutorials:
Lesson: Performing Custom Painting: introductory tutorial to Swing graphics
Painting in AWT and Swing: advanced tutorial on Swing graphics

1) Why is paintComponenet used twice, for the name of the method and as we call a method from super (JPannel)
Here the line super.paintComponent(...), means we want the JPanel to be drawn the usual Java way first (this usually depends on the opaque property of the said JComponent, if it's true, then it becomes the responsibility on the part of the programmer to fill the content area with a fully opaque color. If it is false, then the programmer is free to leave it untouched. So in order to overcome the hassle assoicated with this contract, super.paintComponent(g) is used, since it adheres to the rules, and performs the same task, depending upon whether the opaque property is true or false).
2) What is Graphics g, isn't it just a reference variable for an
object of Graphics since we don't set it equal to = new Graphics();
and
4) The method in my class paintComponent takes the parameter of a
Graphics object but when does paintComponent even get called and when
is the parameter of Graphics inserted
paintComponent method is where all of your painting code should be placed. It is true that this method will be invoked when it is time to paint, but painting actually begins higher up the class heirarchy, with the paint method (defined by java.awt.Component.) This method will be executed by the painting subsystem whenever you component needs to be rendered. Its signature is:
public void paint(Graphics g)
javax.swing.JComponent extends this class and further factors the paint method into three separate methods, which are invoked in the following order:
protected void paintComponent(Graphics g)
protected void paintBorder(Graphics g)
protected void paintChildren(Graphics g)
The API does nothing to prevent your code from overriding paintBorder and paintChildren, but generally speaking, there is no reason for you to do so. For all practical purposes paintComponent will be the only method that you will ever need to override

Drawing Line, Arc etc. Anywhere in the Code Java

I am kind of newbie in Java and in my program, I have to draw some lines, arcs etc. in a function different from paintComponent() in some cases in a class that extends JPanel.
I generally work with ActionScript for visual stuff and I can draw any geometric figure in any functions when I work with AS.
So, is there way to do the same thing in Java, and how?
Thank you!

Why not draw in paintComponent(...)? You state your new, and perhaps you might misunderstand how to do Swing graphics best, so knowing your requirements and the rationale behind them can help us help you.
You can draw on a BufferedImage at any time and in any code
Then that image can be displayed either in a JComponent's paintComponent(...) method
or in a JLabel's Icon via its setIcon(...) method.
Be sure to read the Graphics2D API which will have all the methods needed to do your drawings.
Be sure to read the Swing graphics tutorials because doing this type of work requires a paradigm shift.
Do not get your Graphics object by calling getGraphics() on a component such as a JPanel. Either get it via calling getGraphics() on a BufferedImage or from the paintComponent(Graphics g) parameter.

Java graphics paint method execution flow

I came across this code. I thought I alleviate this confusion before I run into any hiccups along the way in programming. I am having trouble understanding whether the paint or the actionPerformed method gets executed first in Board class. I hope my java comments are correctly stated.
The thing is, I took introductory Java in the summer and graphics was only introduced towards the end of the course. The class used ImageIcon and we never touched the drawImage method and Image abstract class. I also do not understand the paint method at all. This code is more involved than the Java graphics lecture I had. Based on the Java API, the paint method originated from the JComponent class which is JPanel's superclass.
So what is this parameter Graphics g that the paint method takes in all about and how should I think about it? How does the paint method know which object of a graphics class to paint. I looked at the Java API and it says Graphics is an abstract class. How can g be an object if its data type is abstract? I am saying g is an object because the code is calling the drawImage method on the object g.
On a side note, does repaint method mean erase the content in the JPanel and redraw the entire component like rendering?
public class Board extends JPanel implements ActionListener{
private Image apple;
private int apple_x;
private int apple_y;
// over-riding the paint method from the JComponent Class
public void paint(Graphics g){
// recursively call the paint method
super.paint(g);
g.drawImage(apple, apple_x, apple_y, this);
}
// does this method gets called first or the top one?
public void actionPerformed(ActionEvent e) {
repaint();
}
}

Drawing in Java (and basically all current windowing systems) follows the Hollywood principle:
You don't call me; I call you.
I.e. you can tell the system that a certain area will need to be redrawn (repaint()). But you'll have to wait until the system calls you to do the drawing. In Java, the system will call the paint() method and will pass you a Graphics instance to use for drawing.
So the order of event is:
actionPerformed()
paint()
Graphics is often called a graphics context. It's an object used for drawing. Depending on the system and the current requirements, the drawing might go directly on the screen or into an offscreen buffer that is later copied to the screen. The Graphics instance takes care of the details.

Someone can correct me if I am wrong.
Yes, graphics is an abstract class. But an instance of any class that inherits Graphics (such as Graphics2D) can be passed as graphics. If I recall correctly this is call upcasting. g is passed by the UI thread that called paint(), either because the object was invalidated, or has to be updated.
The graphics object is a reference to the actual bitmap that appears to the user.

How to paint outside of paintComponent?

I have a canvas that is drawing everything in a paintComponent() method.
Is it possible to draw outside of paintComponent (without calling a method within paintComponent?)
If so how do you go about doing this?

It depends what you mean and why you need it. For example, it is possible to create a BufferedImage, get the Graphics2D object, Graphics.paint() everything that should be on the image, then drop the image into a JLabel.
But since I do not know what you are trying to achieve (as opposed to what you are trying to do) I cannot know if that answer solves the unstated problem.

I found out how to solve this issue.
What I did was make JPanel an inner class to my JFrame class.
In JPanels paintComponent I had it calling a method from the outer class which did some updating of the graphics, by passing paintComponents Graphics2D object.
This has allowed me to paint "outside" of paintComponent, just as I needed.