How to install JDK on Ubuntu
In this example, we will show you how to install JDK 7 on Ubuntu 12.
P.S This article is updated on 6/12/2012.
1. Find Openjdk
Ubuntu is using OpenJDK, in terminal, issue this command opt-cache search openjdk to search all the available Openjdk version.
$ apt-cache search openjdk default-jdk - Standard Java or Java compatible Development Kit default-jdk-doc - Standard Java or Java compatible Development Kit (documentation) default-jre - Standard Java or Java compatible Runtime default-jre-headless - Standard Java or Java compatible Runtime (headless) icedtea-7-jre-jamvm - Alternative JVM for OpenJDK, using JamVM icedtea-7-plugin - web browser plugin based on OpenJDK and IcedTea to execute Java applets openjdk-7-dbg - Java runtime based on OpenJDK (debugging symbols) openjdk-7-demo - Java runtime based on OpenJDK (demos and examples) openjdk-7-doc - OpenJDK Development Kit (JDK) documentation openjdk-7-jdk - OpenJDK Development Kit (JDK) openjdk-7-jre - OpenJDK Java runtime, using Hotspot JIT openjdk-7-jre-headless - OpenJDK Java runtime, using Hotspot JIT (headless) openjdk-7-jre-lib - OpenJDK Java runtime (architecture independent libraries) openjdk-7-source - OpenJDK Development Kit (JDK) source files java-package - Utility for creating Java Debian packages freemind - Java Program for creating and viewing Mindmaps
2. Install Openjdk
Issue command apt-get install openjdk-7-jdk to install JDK7. Ubuntu will auto download JDK and start the installation, wait a few minutes for the downloading process.
$sudo apt-get install openjdk-7-jdk
3. Verification
Ubuntu installs JDK at /usr/lib/jvm/jdk-folder, for example /usr/lib/jvm/java-7-openjdk-amd64/. In additional, Ubuntu also puts the JDK bin folder in the system path, via symbolic link. For example, /usr/bin/java.
To verify if JDK is installed properly, type java -version.
$java-version java version "1.7.0_09" OpenJDK Runtime Environment (IcedTea7 2.3.3) (7u9-2.3.3-0ubuntu1~12.10.1) OpenJDK 64-Bit Server VM (build 23.2-b09, mixed mode) mkyong@yong-ubuntu:/usr/lib/jvm/java-7-openjdk-amd64/bin$
4. Post-Installation Setup
This step is optional. To configured JAVA_HOME in system path each time the terminal is started, you can append the export JAVA_HOME to /etc/profile or .bashrc.
echo $JAVA_HOME //show nothing $sudo echo "export JAVA_HOME=\"/usr/lib/jvm/java-7-openjdk-amd64/\"" >> ~/.bashrc //restart terminal echo $JAVA_HOME /usr/lib/jvm/java-7-openjdk-amd64/
Done.

You probably forgot to close
tag after "JAVA_HOME" in your blog. It has messed up the formatting below line "in system path each time the terminal is started,"...oops..! it picked up
tag and screwed my comment's formatting also.