I don't know which linux you use, but this has been helpful for me:
http://www.goland.org/Tech/Installing_Java_in_Mandrake_9_1.html This is the adress and underneath is a piece of the file.
Step 2 - Install Java Files -
Open a shell and login as root
You need to run sh on the bin file you downloaded in order to expand it. If you are downloading SDK version 1.4.2 then the command would be: sh j2sdk-1_4_2_01-linux-i586-rpm.bin
This will bring up another long license screen. Press the space bar a couple of hundred times and you will eventually get to a question along the lines of "Do you agree to the above license terms" to which you type in 'yes' (you already gave up your soul in step 1, so there isn't much to lose). This will cause the script you executed to decompress a .rpm file.
To install the RPM file type in "urpmi X" where X is the rpm filename. In the case of 1.4.2 this was "urpmi j2sdk-1_4_2_01-linux-i586.rpm". This will cause files in the RPM to be installed, somewhere.
Step 3 - Setting Up Your Java Environment -
As your normal non-root identity use your favorite editor to open ~/.bashrc
Add in the following path declaration "PATH=$PATH:X:" where X is the location of the bin directory. In my machine this is "PATH=$PATH:/usr/java/j2sdk1.4.2_01/jre/bin:".
Add in the following JAVA_HOME declaration (this tells Java programs where to find the files they need) "JAVA_HOME=X", this is the same X as before so on my system it is "JAVA_HOME=/usr/java/j2sdk1.4.2_01/jre/bin"
Then add in two export statements
export PATH
export JAVA_HOME
Save the file
You are now ready to run Java programs
Step 4 - Setting up Mozilla -
Based on
http://plugindoc.mozdev.org/linux.html: Open a root shell
You need to link the Java plugin file into your Mozilla installation. The command is "ln -s Y/plugin/i386/ns610/libjavaplugin_oji.so Z/plugins/libjavaplugin_oji.so". Where Y is the jre installation directory and Z is the mozilla installation directory. On my machine the command is "ln -s /usr/java/j2sdk1.4.2/jre/plugin/i386/ns610/libjavaplugin_oji.so /usr/lib/mozilla-1.3.1/plugins/libjavaplugin_oji.so"
NOTE: If you are using Mozilla 1.4 or higher you need to get the .so file from the /ns610-gcc32 directory not the /ns610 directory.
Gera