I have downloaded jdk-8u20-linux-i586.tar.gz and extracted using:
tar -xzvf jdk-8u20-linux-i586.tar.gz
Now I'm confused what to do after that.

1. Go to http://slackbuilds.org/repository/14.1/development/jdk/

and download the SlacKBuild for jdk.

2. Once that is saved on your harddrive (assume it is in your home dir), untar it:

tar xvf jdk-7u67-linux-i586.tar.gz
cd jdk-7*gz

3. Bring in the archive file that you have:

mv /path/to/jdk-8u20-linux-i586.tar.gz .


4. Now alter the version that you want to install

sed -i 's/7u67/8u20/g' jdk.SlackBuild


5. And finally, make the SlackBuild executable and execute:

chmod +x jdk.SlackBuild
./jdk.SlackBuild

6. And then install:

su -c "installpkg /tmp/jdk*8u20*t?z"

That is all.

Or read this:
http://docs.slackware.com/howtos:software:java

2 members found this post helpful.

after doing ./jdk.SlackBuild the output is:
mv: cannot stat 'jdk1.7.0_20': No such file or directory

I actually like brianL's answer better, but just to correct my own:

you also need to sed the version number:
sed -i 's/7u67/8u20/g' jdk.SlackBuild
sed -i 's/1.7.0_/1.8.0_/g' jdk.SlackBuild


But brianL's solution is better; I forgot there was a SlackBuild for it in /extras. You ought to use that.

1 members found this post helpful.

Successfully installed java but firefox browser is not configured correctly. I tried which java in terminal the output is:
bash-4.2$ which java
which: no java in (/usr/local/bin:/usr/bin:/bin:/usr/games:/usr/lib/kde4/libexec:/usr/lib/qt/bin:/usr/share/texmf/bin)

---------- Post added 09-18-14 at 07:25 AM ----------

Successfully installed java but firefox browser is not configured correctly. I tried which java in terminal the output is:
bash-4.2$ which java
which: no java in (/usr/local/bin:/usr/bin:/bin:/usr/games:/usr/lib/kde4/libexec:/usr/lib/qt/bin:/usr/share/texmf/bin)

use:
Or logout and login again

How to activate java plugin in firefox. I tried to activate it under tools > add-ons > plugins but java is not listed there.

I've looked around and cannot seem to find a Java application on the internet to test against. Probably just not looking in the right place.

Anyway, maybe see if java.com can see that you have Java installed:
https://java.com/en/download/install...tect=jre&try=1

and also try these steps to selectively enable Java in Firefox:
https://support.mozilla.org/en-US/kb...-trusted-sites