It's not always easy to prove that two things are equivalent. There are the straightforward cases from high school geometry of those stupid proofs that two triangles are equivalent using SAS (Side angle side), ASA, or one of those other rules. But even in geometry equivalence can get more interesting. Consider these three statements.

• Given a line and a point not on that line, there is exactly one line through the given point parallel to the given line.
• The sum of the interior angles of a triangle is 180 degrees.
• The area of a triangle is proportional to the product of its base and height.

Those three statements don't seem related at all and yet they are equivalent. That's where the fun begins. Similarly in programming there are easy cases of programs we know are equivalent. We can change for loops to while loops or replace the names of variables, methods, or classes with friendlier names. Replacing a case statement with a State pattern may be harder to spot. In today's java.net feature we link to Bill Venner's interview with James Gosling about Gosling's new project named Jackpot.

In Analyze this!, Gosling talks about how Jackpot helps programmers analyze, visualize, and refactor programs. Gosling describes an example of a refactoring.

Moving a method isn't just cutting and pasting text. It's a lot more than renaming the parameters and swizzling them around, because you really want to be able to do things like construct forwarding methods. When you construct forwarding methods, they're different from the original methods.

You can't just replace all uses of the forwarding method by uses of the moved method, because they actually behave slightly differently. The difference is usually around what happens when the pivot parameter is null . That can lead you into a deep morass of essentially theorem proving about properties of the code fragments that you're moving, to understand how they behave with respect to null . And you can treat all kinds of code manipulation that way.

In today's featured Weblogs Amy Fowler asks "Would you run in flipflops . Her entry looks at the benefits of having user experience dictate the UI. Her extended example is the Apple iTunes music store whose interface is simple, non-flashy, and intuitive enough that she's buying way more music than she might otherwise. Eitan Suez reviews a recent book written by java.net blogger Will Iverson in the entry "Impressions of 'Mac OS X for Java Geeks'" .

In Also Today, we link to an entertaining way for novice Java programmers to learn more about Java. IBM's Alphaworks site has released CodeRally. In the xml.com article A Survey of APIs and Techniques for Processing XML, Dare Obasanjo looks at curser based and pull model based parsing in addition to the familiar push and tree models SAX and DOM.

Steve Mallett, the Java Today news editor has gathered the following Java Today News Headlines : "Jakarta POI 2.0-pre2 Released", "Jakarta Element Construction Set 1.4.2 Released", "blojsom blogware 1.9.4 released", and "JD4X has gone beta!".

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