If you are on OpenSuSE:
Open yast2 (CLI or GUI), and choose Software -> Software Management, next you'll search for java. Find a version of java that is 1.5.0_06 or better and install it. If java version 1.5 is not in your list then you'll have to add on more software sources (see: AddingSoftwareSources) then try again.
If you are on SLES10:
Download the Java EE 5 SDK from java.sun.com and follow the install instructions. Install path should be /usr/lib/jvm/
Note: Just because Java 5 is installed does not mean it is active.
A Standard Java Directory
If you are manually working with distributions of Java without an installer, all versions of java should end up in the /usr/java directory. Then you create two symbolic links... the "default" and the "latest" link. When linking the java binaries make sure to use the link passing through the /usr/java/default symbolic path. That way you can change which java the system is using by default simply by changing the default link in /usr/java without following the rest of the instructions for /etc/alternatives
This advice only applies if you don't already have a /usr/lib/jvm directory or you aren't relying on RPMs to manage your java versions. I believe later versions of OpenSuse have started to ship with RPMs that set up this /usr/java directory structure. Either way I'll point you at either /usr/lib/jvm or /usr/java as standard directories to use.
$ ls -l
lrwxrwxrwx 1 root root 11 2007-06-13 14:33 default -> jdk1.5.0_09
drwxr-xr-x 9 root root 376 2006-10-12 16:01 jdk1.5.0_09
drwxr-xr-x 10 root root 472 2007-04-23 15:29 jdk1.6.0_01
lrwxrwxrwx 1 root root 21 2007-04-23 15:29 latest -> /usr/java/jdk1.6.0_01
Manipulating the Distro
Fortunately, the SuSE distribution maintainers at Novell have done a good job of separating out the symbolic links for various programs, java being one of them. To activate one version or another of java in the SuSE distributions we can take advantage of the /etc/alternatives directory. By changing the sym links in this directory you change the active version of these programs.
Try the following:
$ whereis java
java: /usr/bin/java /etc/java /usr/lib/java /usr/share/java /usr/share/man/man1/java.1.gz
$ ls -hal /usr/bin/java
lrwxrwxrwx 1 root root 22 2006-06-29 16:06 /usr/bin/java -> /etc/alternatives/java
$ cd /etc/alternatives/
$ ls -hal java*
lrwxrwxrwx 1 root root 35 2006-07-05 10:04 java -> /usr/lib/jvm/java-1_4_2-sun-188.8.131.52/bin/java
lrwxrwxrwx 1 root root 37 2006-08-25 09:53 javac -> /usr/lib/jvm/java-1_4_2-sun-184.108.40.206/bin/javac
lrwxrwxrwx 1 root root 39 2006-08-25 09:53 javadoc -> /usr/lib/jvm/java-1_4_2-sun-220.127.116.11/bin/javadoc
lrwxrwxrwx 1 root root 37 2006-08-25 09:53 javah -> /usr/lib/jvm/java-1_4_2-sun-18.104.22.168/bin/javah
lrwxrwxrwx 1 root root 37 2006-08-25 09:53 javap -> /usr/lib/jvm/java-1_4_2-sun-22.214.171.124/bin/javap
lrwxrwxrwx 1 root root 37 2006-07-05 10:04 javaws -> /usr/lib/jvm/java-1_4_2-sun-126.96.36.199/bin/javaws
Uh oh. We have the wrong version of java active. Is Java 5 even installed?
$ cd /usr/lib/jvm/
java java-1.4.2-sun java-1.5.0-sun jre jre-1.4.2-sun jre-gcj
java-1.4.2 java-1_4_2-sun-188.8.131.52 java-1.5.0-sun-1.5.0_06 jre-1.4.2 jre-1.5.0 jre-sun
java-1.4.2-gcj-184.108.40.206 java-1.5.0 java-sun jre-1.4.2-gcj jre-1.5.0-sun
Yes it is. I see java-1.5.0-sun-1.5.0_06 and that's just the java we need. Let's see what binaries we have...
$ cd java-1.5.0-sun-1.5.0_06/bin
appletviewer HtmlConverter java javap jdb jsadebugd keytool native2ascii rmic servertool
apt idlj javac java-rmi.cgi jinfo jstack kinit orbd rmid tnameserv
ControlPanel jar javadoc javaws jmap jstat klist pack200 rmiregistry unpack200
extcheck jarsigner javah jconsole jps jstatd ktab policytool serialver
... these are the binaries we're going to symbolically link in /etc/alternatives. But, there are already symbolic links in the way we'll need to remove them and then set come back here to recreate the links.
$ pushd .
$ cd /etc/alternatives
$ sudo rm `ls /usr/lib/jvm/java-1.5.0-sun-1.5.0_06/bin`
$ sudo ln -s * /etc/alternatives/
$ cd /etc/alternatives
$ ls -hal java*
lrwxrwxrwx 1 root root 35 2006-07-05 10:04 java -> /usr/lib/jvm/jre-1.5.0-sun/bin/java
lrwxrwxrwx 1 root root 37 2006-08-25 09:53 javac -> /usr/lib/jvm/java-1.5.0-sun/bin/javac
lrwxrwxrwx 1 root root 39 2006-08-25 09:53 javadoc -> /usr/lib/jvm/java-1.5.0-sun/bin/javadoc
lrwxrwxrwx 1 root root 37 2006-08-25 09:53 javah -> /usr/lib/jvm/java-1.5.0-sun/bin/javah
lrwxrwxrwx 1 root root 37 2006-08-25 09:53 javap -> /usr/lib/jvm/java-1.5.0-sun/bin/javap
And now we have the right symbolic links in place. Test the default version of java:
$ java -version
java version "1.5.0_06"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-b05)
Java HotSpot(TM) Server VM (build 1.5.0_06-b05, mixed mode)
good. Now we have the right version active.
NOTE: The Novell software that depends on Java 1.4 should be smart enough to pick out the right JVM for itself given the /usr/lib/jvm directory structure. We've just set the default java to 1.5.0_06 which works fine with our JBoss tools. If there is a problem in the future, knowing where the other JVM are located will be valuable. The word on the street is that Novell's QA couldn't finish their last round of testing in time for release.
NOTE: the environment variable $JAVA_HOME must point to the home directory of the Java install