How to Install JDK 7 on Ubuntu

There are several JDK implementations available for Linux, such as Oracle JDK 7, OpenJDK, Sun JDK 6, IBM JDK and GNU Java Compiler. We shall choose the Oracle JDK 7 (Ubuntu chooses OpenJDK as its default JDK, which is not 100% compatible with Oracle JDK).

Step 1 : Check if JDK has already been Installed
 
Open a Terminal or press Ctrl + Alt + T and issue this command:
 
javac -version
 
If a JDK version number (e.g., "javac 1.7.0_{xx}") appears, JDK has already been installed. You can skip the installation and goto step 3.
 
Step 2 : Download and Install JDK
 
Goto JDK (Java SE) download site at
Select "Java SE 7ux" ⇒ JDK ⇒ Download ⇒ "Accept Licence Agreement" ⇒ Select Linux x86 (for 32-bit system) or Linux x64 (for 64-bit system) "tar.gz" package, e.g., "jdk-7ux-linux-i586.tar.gz". The tarball will be stored in folder "~/Downloads", by default.
We shall install JDK under "/usr/lib/jvm". First, create a directory "jvm" under "/usr/lib" (with superuser authority "sudo"). Open a Terminal and issue these commands:
 
cd /usr/lib
sudo mkdir jvm
 

Extract the downloaded package (Check your downloaded filename!)
 
cd /usr/lib/jvm
sudo tar xvf ~/Downloads/jdk-7ux-linux-i586.tar.gz
 
JDK shall be extracted in a folder "/usr/lib/jvm/jdk_1.7.0_{xx}", where {xx} is the upgrade number.
 
Step 3 : Add JDK's binary directory
 
Add JDK's binary directory ("bin") to the PATH by editing "~/.profile" (or "~/.bash_profile"):
 
cd
gedit .profile
 
Add this line at the end of the file ".profile", replace "{xx}" with the actual number:
 
export JAVA_HOME=/usr/lib/jvm/jdk_1.7.0_{xx}
export PATH=$PATH:$JAVA_HOME/bin
 
Rerun the configuaration file by:
 
cd
source .profile
     
// Check the new settings for JAVA_HOME and PATH
 
echo $JAVA_HOME
    /usr/lib/jvm/jdk_1.7.0_{xx}
 
echo $PATH
    …..:/usr/lib/jvm/jdk_1.7.0_{xx}/bin
 
Step 4 : Use Java under Firefox
 
To use Java under Firefox, you need to enable the so-called "Java Plugin for web browser".
First, create a Mozilla plugins folder in your home directory
 
mkdir ~/.mozilla/plugins
 
Then, create a symbolic link to your Mozilla plugins folder, (check your JDK folder)
 
ln -s /usr/lib/jvm/jdk1.7.0_{xx}/jre/lib/i386/libnpjp2.so ~/.mozilla/plugins/
 
To verify the installation, restart your Firefox and issue URL "about:plugins" to view the status of the plugins.
 
Step 5 : Verify the JDK installation
 
To verify the JDK installation, issue these commands:
 
// Show the Java Compiler (javac) version
 
javac -version
    JDK 1.7.0_07
 
// Show the Java Runtime (java) version
 
java -version
    ……
     
// Show the location of javac and java
which javac
    /usr/lib/jvm/jdk1.7.0_{xx}/bin/javac
 
which java
    /usr/lib/jvm/jdk1.7.0_{xx}/bin/java


 
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