A fun background change with Java Swing

So the essence is as follows:
A new component is created that draws a triangle:

import java.awt.Color; import java.awt.Component; import java.awt.Graphics; import java.awt.Graphics2D; import java.util.Random; public class Triangle extends Component { @Override public void paint(Graphics g) { Random rn = new Random(); Color c = new Color(rn.nextInt(256), rn.nextInt(256), rn.nextInt(256)); Graphics2D g2d = (Graphics2D) g; // холст для рисования int nPoints = 3; int[] xPoints = new int[nPoints + 1]; int[] yPoints = new int[nPoints + 1]; for (int i = 0; i < nPoints; i++) { double angle = 2 * Math.PI * i / nPoints; xPoints[i] = (int) (150 + 175 * Math.sin(angle)); yPoints[i] = (int) (100 - 100 * Math.cos(angle)); } g2d.setColor(c); g2d.fillPolygon(xPoints, yPoints, nPoints); //repaint(); //если раскомментировать - треугольник неистово мигает в основном окне. } } 

A triangle is created and added to the window pane by pressing the button:

 Triangle t = new Triangle(); t.setSize(new Dimension(500, 500)); t.setLocation(new Point((jPanel1.getWidth() - 260) / 2, (jPanel1.getHeight() - 200) / 2)); t.setVisible(true); jPanel1.add(t); 

And another button changes the background of the panel:

 Random rn = new Random(); Color c2 = new Color(rn.nextInt(256), rn.nextInt(256), rn.nextInt(256)); jPanel1.setBackground(c2); 

And the following happens:
When you click on the drawing button of a triangle, a triangle is drawn, when pressed again, it changes the background (in essence, a new object is drawn, we create a new object, and there the background is random).
When you click on the change of the background of the panel - the background color and the panel and ... triangle (sic) change.
Under the debugger you can see that the paint method is called again.

Questions: what dick? Why it happens? Is this normal? How to fix it?