If you want to install JDK / JRE in Ubuntu 14.04 LTS version then just download the archive file jdk1.8.0_66.tar.gz. The file name will be of this type jdk1.8.0_66.tar.gz , after downloading you have to put it in /opt/ directory. Use the following steps to install java 8 manually in Ubuntu 14.04 LTS version from jdk1.8.0_66.tar.gz archive files.
Step1) Know your Linux OS 32/64 bit version by this command
$ uname -m
Step2) Download the proper JDK version from the Oracle site.
Step3) Unzip it & then place it inside /opt/ directory, using the command in terminal window or by using GUI in desktop or where you download the archive. Then place the unzipped folder into /opt/ directory.
Unzip command to unzip the archive into directly /opt/jdk/ directory
tar -zxf jdk1.8.0_66.tar.gz -C /opt/jdk
Here I have unzipped already in my desktop folder /home/diet/Desktop/jdk1.8.0_66/, so now I shall place (move) it from Desktop/jdk1.8.0_66/ to /opt/jdk1.8.0_66/ directory.
To do that I am using the following command:
root@ubuntu1404lts-hpnotebook:/home/diet/Desktop# mv jdk1.8.0_66/ /opt/
Step4) Set this installation as default JDK , JAVA , JAVAC , JAR etc by the following commands
$ update-alternatives –install /usr/bin/java java /opt/jdk1.8.0_66/bin/java 1072
$ update-alternatives –install /usr/bin/javac javac /opt/jdk1.8.0_66/bin/javac 1072
$ update-alternatives –install /usr/bin/jar jar /opt/jdk1.8.0_66/bin/jar 1072
Step5) Then verify your installation by the following command
update-alternatives --display java
update-alternatives --display java
c
update-alternatives --display jar
Here is an excellent tutorial on it: