What It Means to “Install Java”

So many meanings, so many acronyms

Java terminology at times can be really ambiguous. Here is an attempt to clarify some of the absolute basics, and to help make it a little more obvious how to “install java” on your machine so you can write Java programs.

If you want to write Java programs, you need to get Java on your machine. However, when people talk about “installing Java” on your machine, there are two different things they could mean:

• First, they might mean that you should install what we might call the program runner — that is to say, an application on your machine that runs/executes Java programs. In the Java world, this is called the JRE, short for Java Runtime Environment.
• Second, they might mean that you should install what we might call the program maker — that is to say, an application (or rather, a set of applications) on your machine that can take Java source code and make it into a program. This is called the JDK, short for Java Development Kit.

If you run OS X or Linux, you very well might have the JRE installed already. But if you want to write Java programs, you really need to get the JDK, so you can build programs.

Fortunately, the Java world lets you do that fairly easily. But, here we have yet another ambiguity. There are two versions of the JDK:

• The PAID VERSION: this is called J2EE, or sometimes just JEE, short for Java Enterprise Edition. It is also sometimes abbreviated as EE, short for Enterprise Edition.
• The FREE VERSION: this is called JSE, short for Java Standard Edition. This is sometimes abbreviated merely as SE, short for Standard Edition.

So, suppose we want to install the free version of the JDK. Here’s how.

On OS X, go to this page and download the most recent JDK:
http://www.oracle.com/technetwork/java/javase/downloads/index.html

On Ubuntu, you can use apt-get. Make sure you update your apt-get databases, then install the open jdk 1.7 package:

$ sudo apt-get install openjdk-7jdk

On Fedora/CentOS, you can use yum. Make sure you update your yum databases, then install the open jdk 1.7.0 package:

$ sudo yum install java-1.7.0-openjdk

Next, let’s confirm that you have the tools installed. First, let’s see if you have “java” (this is the JRE). Open a terminal, and type:

$ which java

If nothing is printed out, you don’t have the JRE. If you see something printed out like this:

$ /usr/bin/java

then you know you have the JRE installed.

Second, see if you have javac, short for the Java Compiler. In a terminal, type:

$ which javac

If nothing is printed out, you likely don’t have the JDK installed. But if you have something printed out like this:

$ /usr/bin/javac

then you can be reasonably certain you have the JDK installed. And then, you can start writing Java programs (if you are so inclined).