Paint method

[subbus]

how to fetch a value from a text box from FormUi class and send to the paint(Graphics g) method in Paint.class?

[Fubarable]

how to fetch a value from a text box from FormUi class

What is a "text box"?
What is the "FormUi class"?

.. and send to the paint(Graphics g) method in Paint.class?

What is the Paint class?

Perhaps you want to tell us the details of your problem?

[subbus]

I have two class files formUI and paint. formUI has text box component from which i need to fetch the string value and pass it on to the paint(Graphics g) method.

[Fubarable]

I have two class files formUI and paint. formUI has text box component from which i need to fetch the string value and pass it on to the paint(Graphics g) method.

OK, but I'm assuming that you've got a Swing application, and I thought I knew all of the standard Swing components in existence in particular the text components, but I've never heard of a "text box". Can you clarify this some more.

As for the gist of your question, the devil's in the details: how you extract information will depend much on the program code and overall structure, things we still know nothing about. Again, you may wish to tell us much more of the details about your problem and your code. You're almost asking it as if we have magic that allows us to see the code you've not shown and be able to understand problems that you've not stated. I wish we had these abilities, but unfortunately, we don't.

[subbus]

public class Ex1 extends JDialog{
	
	JDialog dlg=new JDialog();
	JTextField txt=new JTextField(10);
	JButton click=new JButton("Print");
	String mesg;
	PaintScreen p=new PaintScreen();
	public void drawEx1() {
		dlg.setLayout(new FlowLayout());
		dlg.add(txt, FlowLayout.LEFT);
		dlg.add(click, FlowLayout.LEFT);
		click.addMouseListener(new MouseAdapter() {
			public void mouseClicked(MouseEvent me)
			{
				call();
			}
		});
		dlg.setSize(100, 100);
		dlg.setVisible(true);
	}
	public void call()
	{
		mesg=txt.getText();
		p.display(mesg);
		
		
	}
	
	public static void main(String[] a)
	{
		Ex1 obj=new Ex1();
		obj.drawEx1();
		
	}

}

public class PaintScreen extends JDialog {
	
	String name="";
	JDialog dlg;
	   void display(String mesg)
	   {
		   name=mesg;
		   System.out.println("passed value:"+name);
		   dlg=new PaintScreen();
		   dlg.setSize(200, 200);
		   dlg.setVisible(true);
		   
	   }
	 public void paint(Graphics g)
	 {
		 
		 
		 g.drawString(name, 100, 50);
// here i am getting a null pointer exception
	 }
}

[Norm]

To see some of what your code is doing(start of debugging), change the value of the name variable:
String name="Initial value";