confused with java graphics paint

Question

i am very bigginer to java .i trying to draw a line in a jpanel (using netbean ide)..i read some articles .but problem is it draw thais line without calling it .i want to draw l

Answer 1

Problem: You have no event code in your button event handler.

1. Try creating a state variable called boolean showLine before your constructor.
2. Initialize it to false in constructor.

3. Modify state variable on button click.

   private void jButton1ActionPerformed(
                   java.awt.event.ActionEvent evt) {                                         
   Graphics gg = null;
   // TODO add your handling code here:
   showLine = (true) ? false : true;
   

   }

4. Add condition checking to paint method.

   @Override public void paint(Graphics g) { Graphics2D ga = (Graphics2D)g;

   if (showLine) {
       ga.setPaint(Color.red);
       ga.drawLine(200,100,200,300);
   }
   

   }