Java

Java is a general-purpose computer programming language that is concurrent, class-based, object-oriented, and specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere" (WORA), meaning that compiled Java code can run on all platforms that support Java without the need for recompilation. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of computer architecture.

Java was originally developed by James Gosling at Sun Microsystems (which has since been acquired by Oracle Corporation) and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from [C and C++], but it has fewer low-level facilities than either of them.

As of 2016, Java is one of the most popular programming languages in use, particularly for client-server web applications, with a reported 9 million developers, although there's been an effort to push away from using Java and Flash applications in web browsers for [HTML5].

Java and JavaScript are two different languages and are NOT interchangable!

Installing Java on the Raspberry Pi

The Free Software Foundation would rather you install OpenJDK and IcedTea because of the whole GNU thing. However, nothing beats the real thing when it comes to installing Java. And the Java Team at Oracle (many of whom used to work at Sun) has been more than cool with using Java on Raspberry Pi. The best part, it is full Java. Not the crappy version of Java, Java ME, that was made for mobile devices back in the 2000s (although the original Motorola RAZR still has a place in my heart).

Java has a version of Java 8 for ARM architecture. Built for Raspberry Pi, this version of Java also works for Odroid!

CAUTION These instructions may be out of date. They are still good for something though.

1. Start by going here: http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
2. Accept Oracle's Binary Code License Agreement.
3. Download Java SE Development Kit 8 Update 73 for Linux ARM v6/v7 Hard Float ABI, the file I downloaded was called jdk-8u73-linux-arm32-vfp-hflt.tar.gz which I downloaded to the directory ~/Software.
4. tar -xzvf jdk-8u73-linux-arm32-vfp-hflt.tar.gz. By extracting it in the ~/Software directory, we don't need to change the permission for us to use.
5. sudo mv jdk1.8.0_73/ /opt/. Move it to the /opt/ directory.
6. Set default java and javac to the new installed jdk8.

```
$ sudo update-alternatives --install /usr/bin/javac javac /opt/jdk1.8.0_73/bin/javac 1
$ sudo update-alternatives --install /usr/bin/java java /opt/jdk1.8.0_73/bin/java 1
$ sudo update-alternatives --config javac                    # Select 1
$ sudo update-alternatives --config java                     # Select 1
```

7. We verify with the commands with -verion option.

```
javac -version
java -version
```

8. Finally, we set our $JAVA_HOME variable and add Java to our $PATH variable. This is necessary because some Java basedapplications require a $JAVA_HOME variable. We will need to set this system-wide so we will need to create /etc/profile.d/jdk.sh. You will need to use vim or nano to create this file as trying to do it the sudo bash -c "echo 'something'" way doesn't work so well with variables.

```
export JAVA_HOME=/opt/jdk1.8.0_73
export PATH=$JAVA_HOME/bin:$PATH
```

9. Start a new terminal. You should see $JAVA_HOME/bin as part of $PATH and have $JAVA_HOME echo the path of Java now.
10. Reboot. You need to do this to make sure root know about the new variables or else things like Ant and Maven won't install when we try to install JRuby.

TODO: Create a java file to test.

TODO: Show instructions for compiling and executing.

See Also

• GCC - gcc and g++
• Perl
• Python
• Ruby
• Node
• Haskell
• OCAML
• JRuby
• Scala (You defintely have to read this one!)

External Links

• http://java.com/en/download/
• http://www.oracle.com/technetwork/java/javase/downloads/jdk8-arm-downloads-2187472.html