Java class file: Difference between revisions

Revision as of 20:43, 18 November 2005

Revision as of 23:24, 22 November 2005

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Since JVMs are available for many [[platform (computing)|platform]]s, the .class file compiled in one platform will execute in a JVM of another platform. This makes Java platform-independent.

Class files are identified by the following 4 [[byte]] [[header (information technology)|header]] ([[[[in [[hexadecimal]]]]]]): <code>CA FE BA BE</code>.

The history of this [[Magic number (programming) | magic number]] was explained by [[James Gosling]]:

<BLOCKQUOTE>

"We used to go to lunch at a place called St Michael's Alley. According to local legend, in the deep dark past, the Grateful Dead used to perform there before they made it big. It was a pretty funky place that was definitely a Grateful Dead Kinda Place. When Jerry died, they even put up a little Buddhist-esque shrine. When we used to go there, we referred to the place as Cafe Dead. Somewhere along the line it was noticed that this was a HEX number. I was re-vamping some file format code and needed a couple of magic numbers: one for the persistent object file, and one for classes. I used CAFEDEAD for the object file format, and in grepping for 4 character hex words that fit after "CAFE" (it seemed to be a good theme) I hit on BABE and decided to use it. At that time, it didn't seem terribly important or destined to go anywhere but the trash-can of history. So CAFEBABE became the class file format, and CAFEDEAD was the persistent object format. But the persistent object facility went away, and along with it went the use of CAFEDEAD - it was eventually replaced by RMI."

</BLOCKQUOTE>

==References==

* James Gosling private communication to Bill Bumgarner: http://bbum.pycs.net/2003/01/28.html

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