Re: Question about casts
Peter Duniho wrote:
On Mon, 18 Feb 2008 18:05:13 -0800, Lew <lew@lewscanon.com> wrote:
[...]
There is a lot of information googlable, I just picked the top couple
of links I found in researching for this post.
Well, I do appreciate you sharing those links. They are all useful and
informative.
However, I am having the same problem with these that I have had with
other issues (see the previous EDT thread). That is, none of these are
what I'd consider authoritative (except the Graphics2D class
documentation, which fails to discuss the parameter passed to the
paint() method so doesn't address this specific question at all), nor do
they clearly state that this is behavior that can be relied upon not to
change.
The one from sun.com can safely be considered authoritative. After all, it is
part of their official documentation, under the heading "Reference".
You are right that they do not guarantee to keep it that way, but they haven't
changed it in the last ten years - it's been since version 1.2. Given the
care they took not to invalidate the original guarantee that those parameters
would be of type 'Graphic' I think we're safe. For a little while, at least.
<http://java.sun.com/developer/technicalArticles/GUI/java2d/java2dpart1.html>
With the Java 2 platform, you can do this by casting the Graphics class that is
passed in to your custom component's paint methods to a java.awt.Graphics2D object,
using it to render the appropriate shapes:
public paint(Graphics g) {
Graphics2D g2 = (Graphics2D)g;
<http://java.sun.com/j2se/1.5.0/docs/guide/2d/spec/j2d-intro.html#wp61978>
To ensure backward compatibility, the functionality of existing JDK graphics and
imaging classes and interfaces was maintained. Existing features were not removed
and no package designations were changed for existing classes. The Java 2D API
enhances the functionality of the AWT by implementing new methods in existing
classes, extending existing classes, and adding new classes and interfaces that
don2"t affect the legacy APIs.
....
To gain access to the new features implemented in Graphics2D, a Java 2D API2 compatible applet
casts the graphics context to a Graphics2D object:
public void Paint (Graphics g) {
Graphics2D g2 = (Graphics2D) g;
...
...
g2.setTransform (t);
}
Boy, Sun just keeps repeating that information over and over in different
articles. They must really mean it. That one that says "spec" looks pretty
official, too, except for the misspelling of 'Paint'. I found it by a link on
Sun's Java 2D FAQ page.
What the heck, let's look for a tutorial:
<http://java.sun.com/docs/books/tutorial/2d/overview/rendering.html>
To use Java 2D API features, you cast the Graphics object passed into a
component2"s rendering method to a Graphics2D object. For example:
public void paint (Graphics g) {
Graphics2D g2 = (Graphics2D) g;
...
}
I admit, it took me about twenty minutes to find these references.
--
Lew