GCJ

GCJ is an effort by the GCC team to provide an open source Java compiler and runtime environment to interpret Java bytecode. Unfortunately, the GCJ runtime environment is not an environment that is often tested on by Eclipse developers.

The most common problems surrounding GCJ are: -Eclipse does not start at all -Eclipse throws a 'java.lang.ClassNotFoundException: org.eclipse.core.runtime.Plugin' that can be found in the logs (located in workspace/.metadata/.log)

The workspace's log file is a good place to check to identify whether GCJ is being used or not. Every Eclipse log session should be prepended with information about the runtime environment that was used to run Eclipse. The log may include something like the following:

java.fullversion=GNU libgcj 4.2.1 (Debian 4.2.1-5)

If Eclipse does start, one can check which runtime environment is being used to run Eclipse by going to 'Help > About Eclipse SDK > Configuration Details'. The About Dialog itself can also provide other information, the build identifier can be of particular interest as it is tagged by some distros. This allows the user to identify whether Eclipse was downloaded through the distribution's package management system or directly from the eclipse.org website.

Eg: Build id: M20070212-1330 (Ubuntu version: 3.2.2-0ubuntu3)

The two most common workarounds would be to:

To download Eclipse, try one of the links below:

It is imperative that 64-bit builds are downloaded and used if a 64-bit Java runtime environment has been installed. Below are two sample tarball names of version 3.3.2 of the Eclipse SDK packaged for 32-bit and 64-bit processors.
eclipse-SDK-3.3.2-linux-gtk.tar.gz (32-bit)
eclipse-SDK-3.3.2-linux-gtk-x86_64.tar.gz (64-bit)

To run Eclipse with an alternate Java runtime environment, the path to the Java virtual machine's binary must be identified. With an Eclipse installation from the distribution, altering the $PATH variable to include the path to the alternate Java runtime environment is often not enough as the Eclipse that Linux distributions package often performs a scan internally to pick up GCJ by itself whilst ignoring what's on the $PATH. An example of the terminal's output can be seen below:

searching for compatible vm...
testing /usr/lib/jvm/java-7-icedtea...not found
testing /usr/lib/jvm/java-gcj...found

Once the path to the virtual machine's binary has been identified, try running Eclipse with the following command:

./eclipse -vm /path/to/jre/bin/java

For an actual example, it might look something like the following:

./eclipse -vm /usr/lib/jvm/sun-java-6/bin/java
./eclipse -vm /opt/sun-jdk-1.6.0.02/bin/java

If this seems to solve the problem, it is likely that the problem really was related to the use of GCJ as the Java runtime for running Eclipse. The eclipse.ini file located within Eclipse's folder can be altered to automatically pass this argument to Eclipse at startup. An example of its content is presented below:

-showsplash
org.eclipse.platform
--launcher.XXMaxPermSize
256m
-vm
/opt/sun-jdk-1.6.0.02/bin/java
-vmargs
-Xms40m
-Xmx512m

Note that every argument must be on its own line. More information about the eclipse.ini file can be found at http://wiki.eclipse.org/Eclipse.ini.

If problems persists after downloading an installation of Eclipse from eclipse.org and using a supported Java runtime environment (a list of which may be found in the readme_eclipse.html supplied with your installation), one should seek assistance from the Eclipse team via its plethora of communication channels like the newsgroups, the IRC channel, and/or bugzilla.