Graphics

• To draw something in a component, you need to get a Graphics context for the component, that is, an associated instance of the Graphics class. You can do this with the method getGraphics(), which takes no arguments.
• To tell a component how to paint itself, you should redefine the paintComponent() method for the component. You will need to define a class for the component to do this. paintComponent() takes the Graphics context as its argument. For example, the following would draw a small red rectangle in the middle of the component.
  public void paintComponent(Graphics g) {
    g.setColor(Color.RED);
    g.fillRect(getWidth() / 2 - 5,
               getHeight() / 2 - 5, 10, 10);
  }
• Once you have redefined paintComponent, you can call repaint() anywhere in your code; this will cause paintComponent() to be called in the component and in any components that it contains. repaint() is also automatically called when the component is displayed, for example, when it (or the component that it is contained in) is de-iconized.
• Here are other Graphics methods you may need. Each of the "draw" methods for a figure corresponds to a "fill" method, which does the same thing except that it fills the figure with the current color.
  clearRect(int x, int y, int width, int height)
  drawLine(int x1, int y1, int x2, int y2)
  drawRect(int x, int y, int width, int height)
  drawOval(int x, int y, int width, int height)
  drawPolygon(int[] xPoints, int[] yPoints, int nPoints)
  drawString(String str, int x, int y)
  setColor(Color c)
  setFont(Font font)

© 2004. Indiana University and Michael Gasser. www.indiana.edu/~gasser/Q530/Notes/graphics.html 10 Nov 2004