Fill-in color on triangle using mouse click

I was wondering how to fill in a triangle shape with color when a user click on the triangle.

So far I am using txt file as input file to read the coordinate of the triangle to be drawn on screen.

From stackoverflow

• I did something like this long ago .. here's something that might help

• Not sure what your "environment is"...

  Extend a JPanel.
  Add an MouseAdapter to capture the coordinates in the mouseClicked method and save them in an array in your panel.
  Override the drawComponent method to draw the triangle. Something like

  class MyPanel extends JPanel {
      private int count = 0;
      private Point[] points = new Point[3];
  
      MyPanel() {
          setBackground(Color.WHITE);
          addMouseListener(new MouseAdapter() {
              @Override
              public void mouseClicked(MouseEvent e) {
                  if (e.getButton() == MouseEvent.BUTTON1) {
                      if (count == points.length) {
                          for (int i = 1; i < points.length; i++) {
                              points[i-1] = points[i];
                          }
                          count -= 1;
                      }
                      points[count] = e.getPoint();
                      count += 1;
                      repaint();
                  }
              }
          });
      }
  
      @Override
      protected void paintComponent(Graphics g) {
          super.paintComponent(g);
          Graphics2D gg = (Graphics2D) g;
          if (count > 2) {
              Polygon polygon = new Polygon();
              for (int i = 0; i < count; i++) {
                  polygon.addPoint(points[i].x, points[i].y);
              }
              gg.setColor(Color.BLUE);
              gg.fill(polygon);
          }
      }
  }
  

  It's not complete, but ...