title: Drawing a rectangle that won't disappear in next paint
body: <p>I trying to create a JPanel that draws rectangles. The Panel needs to draw alot of rectangles, but they dont move.
  One solution to my problem was to create an list with all the rectangles i already created and draw they all in every call of "Paint". But there is a lot of rectangles and it slows the computer.<br>
  I also tried to use repaint(x, y, height, width) to rapaint just the space of the new rectangle but it did not work. (JPanel keeps erasing previous rectangles.)
  In sort, i need to draw rectangles that wont disappear every paint. Or a paint method that wont erase previous draws, or wont paint the background.
  That is part of my JPanel class:</p>
  
  <pre><code>class MyPanel extends JPanel{
    private int x, y, size;
    private Color c;
    public void DrawRect(int x, int y, int size, Color c){
        this.x = x;
        this.y = y;
        this.size = size;
        this.c = c;
        repaint();
    }
    @Override
      public void
      paint(Graphics g) {
  
          g.setColor(c);
        g.fillRect(x, y, size, size);
      }
  </code></pre>
  
  <p>}</p>