Repaint() doesn't call paintComponent()

Question

first I wnt to mention that these are my first steps in java.
I want to create a rectangle to select a region, therefore I get the position of the mouse, what's already working :)
but i'd like to paint the rectangle when the mouse is clicked. so I thought to call paintComponent() with repaint(), but paintComponent() don't get called. I'm confused and cannot understand what is happeneing there :(
the code:
public class CPaintRect extends JPanel implements MouseListener{
     public int startX, startY;
     public int endX, endY;
     int u = 10;
     public CPaintRect() {
          System.out.println("CpaintRect");
     public void actionPerformed(ActionEvent e){
          this.repaint();
     public void mouseClicked (MouseEvent e){
     public void mouseEntered (MouseEvent e){
     public void mouseExited (MouseEvent e){
     public void mousePressed (MouseEvent e){
          startX = (int) e.getX();
          startY = (int) e.getY();
          System.out.println(startX + " " + startY);
          repaint();
     public void mouseReleased (MouseEvent e){
          endX = e.getX();
          endY = e.getY();
          repaint();
          //System.out.println("position: " + selection);
     public void paintComponent(Graphics g) {
          u+=10;
          System.out.println("paint"); //-->not shown
          g.setColor(Color.red);
          g.drawRect(0, 0, u, u); //just as test           g.drawRect(startX, startY, endX-startX, endY-startY);
sorry for my english, and thanks in advance

Answer 1

You forgot to add the mouseListener
In the constructor, aftet this line System.out.println("CpaintRect");
     addMouseListener(this);
Noah