In Java, repaint() doesn't call paintcomponent()

Question

For a homework assignment I have to make a Java program that draws a red circle on a jframe when clicking a "start" button. When clicking the button, the method setSmallCircle is called. This does work, but inside this method I'm making a calling repaint() , but this doesn't seem to call the paintComponent method.

This is my code so far:

import java.awt.*;
import javax.swing.*;
class ReactionPanel extends JPanel {
  Color color;
  int size;
  public void paintComponent(Graphics g){
    System.out.println("paintcomp 1");
    super.paintComponent(g);
    System.out.println("paintcomp 2");
    g.setColor(color);
    g.fillOval(200, 200, size, size);
  }
  public void setSmallCircle(Color c){
    color = c;
    size = 10;
    System.out.println("drawing");
    repaint();
    System.out.println("repaint called");
  }
}

The method setSmallCircle(Color.red) is called by some other class. Does anyone know why the "repaint()" isn't drawing a red circle?

Answer 1

Any update to the painting of swing component should be inside EDT (eevent dispatch thread) . However while experimenting following portion:

public void paintComponent(Graphics g){
    System.out.println("paintcomp 1");

    super.paintComponent(g);
    g.setColor(color);
    System.out.println(color); // print color as null
    g.fillOval(20, 20, size, size); // printing size as 0

    System.out.println(size);

  }

updating color and size in setSmallCircle() is not taking effect !! paintComponent seems to keep using the old value, instead of updated value.