Novice graphics question

[Dennis Noren]

I'm using paintComponent within a class that extends Jcomponent (using Java2 1.4.2). I'm using graphics2D by:

public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D)g;
...

I can access all the advertised methods from there. However, I need to build some compound objects with common structure, but vary the characteristics of elements within the objects, for example, different colors, linetypes, rotations, etc. I know how to use GeneralPath, Area, intersect, add, etc. to manipulate these elements, but I need to create many of these compound objects with the flexibility of making the separate elements within the objects look different as needed. The first thing I think of is to build methods with arguments for what I want to vary. However, within those methods I cannot use the methods that manipulate the graphics object, apparently, and I that isn't thinking the OO way, methinks.

Is the use of an inner class advised here? I know that gives me access to data and instances of the surrounding class. Or is it better to use an external class, and if so, can I pass a reference to be able to access the graphics object? I'm not quite sure how to go about this and haven't been able to find examples of it.

Yes, I have taken intro classes in OOA and OOD, and an intro Java class, but it doesn�t all stick at once. ;-)

Thanks for any help you can offer.

[Ernest Friedman-Hill]

Hi Dennis,

Welcome to JavaRanch!

The general shape of the solution would look like this:

class MyGraphicsWindow extends JComponent {
  ...
  private ArrayList m_shapes;
  public void paintComponent(Graphics g) {
    for (i=0; i<m_shapes.size(); ++i) {
      MyShape shape = (MyShape) m_shapes.get(i);  
      shape.draw(g);
    }
  }
}
 
interface MyShape {
  void draw(Graphics g);
}
 
class Circle implements MyShape {
  int radius;
  Circle(r) { radius = r; }
  public void draw(Graphics g) {
    // I didn't take the time to look up the right
    // method and/or arguments here, so forgive me
    g.fillOval(0, 0, radius*2, radius*2);
  }
}
 
class Square implements MyShape ...

Note that instead of creating your own interface MyShape, you can actually have your shapes be JComponents themselves and extend JComponent!
[ January 07, 2005: Message edited by: Ernest Friedman-Hill ]

[Simon Hunt]

Dear Earnest

Just a quick "thank you". This post solved an embarassingly simple problem I was having with trying to output a group of objects to a Jpanel, whilst trying to keep their graphics behaviour inside the objects.

The problem: I was only able to see one object at a time (the last one). This post finally got me to realise that I needed to be painting them all on the _same_ panel. :roll:

Cheers!

Simon*