Eric Burke has fallen into a pattern while trying to use Java generics:

Eric Burke:
... I foolishly tried this:
... Oops. Won’t compile.
... Foiled by erasure!

Brian Gilstrap, who's also experimenting with generics, has coined a name for this phenomenon—The Wall Of Erasure.

In plain English: Every really cool idea involving Java generics will invariably lead to insurmountable difficulties the root cause of which is erasure.

Responses[3]

Posted by Weiqi Gao on November 4, 2007 10:06:26 PM CST #

All the noise about Leopard and Java6 last week made me thinking: Does my favorite operating systems include the JDK? And if so, which version?

The answer, of course, is that Windows does come with a JRE, but it's at version 1.1; and that Debian comes with a incomplete open source JRE that's roughly at version 1.4.

Debian 4.0, however, makes getting the higher versions of Java easy. Sun Java 5 is available in Debian 4.0's stable software repository, while Sun Java 6 is available in the Debian unstable software repository. Since neither are free software, they can only be found in the non-free section of the repositories.

Enabling the non-free section of the stable repository in very easy, as I documented here 136 days ago.

Enabling the unstable repository in Debian 4.0 is something that I don't want to do lightly, for I don't want to upgrade every package in my system to the bleeding edge, at least not yet. Jonathan mentioned "APT pinning" when I asked him about this at the time. And learning about APT pinning I did yesterday.

The three degrees of APT pinning

I have gone through three documents that I found on the Google about APT Pinning.

First there's the very clear Apt-Pinning for Beginners. It outlines exactly what to do to enable the testing and unstable repositories in Debian in such a way as to favor the stable repositories's contents.

But I have some unanswered questions, so I went to the Debian Wiki's AptPinning page. It provided a few more recipe's of doing APT pinning. I particularly like the "only if I say so" approach.

But I still have some unanswered questions, so I went to the authoritative source—the man page of apt_preferences(5). This man page is on my hard drive all along. And to read a printed out copy I issued the command

[weiqi@gao]$ man -Tps apt_preferences | lpr

This six-page document contains explanations of every detail of the things that I need to do.

The steps

Here's the steps I took to get Sun JDK 6 to my Debian GNU/Linux 4.0 system (the right way):

1. Add a line to /etc/apt/sources.list:

   # deb cdrom:[Debian GNU/Linux 4.0 r0 _Etch_ - Official amd64 DVD Binary-1 200704
   07-12:15]/ etch contrib main
   
   deb cdrom:[Debian GNU/Linux 4.0 r0 _Etch_ - Official amd64 DVD Binary-1 20070407
   -12:15]/ etch contrib main
   
   deb http://ftp.debian.org/debian/ etch main non-free
   deb-src http://ftp.debian.org/debian/ etch main non-free
   
   deb http://security.debian.org/ etch/updates main contrib non-free
   deb-src http://security.debian.org/ etch/updates main contrib non-free
   
   deb http://www.debian-multimedia.org etch main
   deb http://www.dipconsultants.com/debian etch main
   
   ### unstable #######
   deb http://ftp.debian.org/debian/ unstable main non-free

2. Add a line to /etc/apt/apt.conf.d/70debconf:

   // Pre-configure all packages with debconf before they are installed.
   // If you don't like it, comment it out.
   DPkg::Pre-Install-Pkgs {"/usr/sbin/dpkg-preconfigure --apt || true";};
   APT::Cache-Limit "100000000";

3. Created /etc/apt/preferences:

   Package: *
   Pin: release a=stable
   Pin-Priority: 700
   
   Package: *
   Pin: release a=unstable
   Pin-Priority: 600

4. Run apt-get update
5. Install the eight sun-java6-* packages
   • sun-java6-bin
   • sun-java6-demo
   • sun-java6-doc
   • sun-java6-fonts
   • sun-java6-javadb
   • sun-java6-jdk
   • sun-java6-jre
   • sun-java6-source
   with

   [root@gao]# feta install <package-name>s

   Notice that the sun-java6-doc package requires that I download the JDK documentation from Sun's Java download site and put the zip file in /tmp.

Responses[14]

Posted by Weiqi Gao on November 4, 2007 9:31:22 AM CST #