Assumptions:

• An Oracle JDK has been installed.
• The JDK was installed to the default directory.

Setup steps

Add a **New System Variable** by clicking the New... button in **System Variables** with the name `JAVA_HOME` and whose value is the path to the directory where the JDK was installed. After entering these values, press OK. [](https://i.stack.imgur.com/E4c2M.png)

It is better to append at the begining of the line because Oracle's software used to register their own version of Java in Path - This will cause your version to be ignored if it occurs after Oracle's declaration.

Check your work

1. Open the command prompt by clicking Start then typing cmd and pressing Enter.
2. Enter javac -version into the prompt. If it was successful, then the version of the JDK will be printed to the screen.

Note: If you have to try again, close the prompt before checking your work. This will force windows to get the new version of Path.

Using the Package Manager

JDK and/or JRE releases for OpenJDK or Oracle can be installed using the package manager on most mainstream Linux distribution. (The choices that are available to you will depend on the distro.)

As a general rule, the procedure is to open terminal window and run the commands shown below. (It is assumed that you have sufficient access to run commands as the "root" user ... which is what the sudo command does. If you do not, then please talk to your system's administrators.)

Using the package manager is recommended because it (generally) makes it easier to keep your Java installation up to date.

apt-get, Debian based Linux distributions (Ubuntu, etc)

The following instructions will install Oracle Java 8:

$ sudo add-apt-repository ppa:webupd8team/java
$ sudo apt-get update
$ sudo apt-get install oracle-java8-installer

Note: To automatically set up the Java 8 environment variables, you can install the following package:

$ sudo apt-get install oracle-java8-set-default

Creating a .deb file

If you prefer to create the .deb file yourself from the .tar.gz file downloaded from Oracle, do the following (assuming you've downloaded the .tar.gz to ./<jdk>.tar.gz):

$ sudo apt-get install java-package # might not be available in default repos
$ make-jpkg ./<jdk>.tar.gz          # should not be run as root
$ sudo dpkg -i *j2sdk*.deb

Note: This expects the input to be provided as a ".tar.gz" file.

slackpkg, Slackware based Linux distributions

sudo slapt-get install default-jdk

yum, RedHat, CentOS, etc

sudo yum install java-1.8.0-openjdk-devel.x86_64

dnf, Fedora

On recent Fedora releases, yum has been superseded by dnf.

sudo dnf install java-1.8.0-openjdk-devel.x86_64

In recent Fedora releases, there are no packages for installing Java 7 and earlier.

pacman, Arch based Linux distributions

sudo pacman -S jdk8-openjdk

Using sudo is not required if you're running as the root user.

Gentoo Linux

The Gentoo Java guide (opens new window) is maintained by the Gentoo Java team and keeps an updated wiki page including the correct portage packages and USE flags needed.

Installing Oracle JDKs on Redhat, CentOS, Fedora

Installing JDK from an Oracle JDK or JRE tar.gz file.

tar xzvf jdk-8u67-linux-x64.tar.gz

Installing from an Oracle Java RPM file.

$ sudo rpm -ivh jdk-8u67-linux-x644.rpm 

Oracle Java 7 and Java 8

Java 7 and Java 8 for macOS are available from Oracle. This Oracle page answers a lot of questions about Java for Mac. Note that Java 7 prior to 7u25 have been disabled by Apple for security reasons.

In general, Oracle Java (Version 7 and later) requires an Intel-based Mac running macOS 10.7.3 or later.

Installation of Oracle Java

Java 7 & 8 JDK and JRE installers for macOS can be downloaded from Oracle’s website:

• Java 8 - Java SE Downloads (opens new window)
• Java 7 - Oracle Java Archive. (opens new window)

After downloading the relevant package, double click on the package and go through the normal installation process. A JDK should get installed here:

/Library/Java/JavaVirtualMachines/<version>.jdk/Contents/Home

where corresponds to the installed version.

Command-Line Switching

When Java is installed, the installed version is automatically set as the default. To switch between different, use:

export JAVA_HOME=/usr/libexec/java_home -v 1.6 #Or 1.7 or 1.8

The following functions can be added to the ~/.bash_profile (If you use the default Bash shell) for ease of use:

function java_version {
   echo 'java -version';
}

function java_set {
   if [[ $1 == "6" ]]
   then
       export JAVA_HOME='/usr/libexec/java_home -v 1.6';
       echo "Setting Java to version 6..."
       echo "$JAVA_HOME"
   elif [[ $1 == "7" ]]
   then
       export JAVA_HOME='/usr/libexec/java_home -v 1.7';
       echo "Setting Java to version 7..."
       echo "$JAVA_HOME"
   elif [[ $1 == "8" ]]
   then
       export JAVA_HOME='/usr/libexec/java_home -v 1.8';
       echo "Setting Java to version 8..."
       echo "$JAVA_HOME"
   fi            
}

Apple Java 6 on macOS

On older versions of macOS (10.11 El Capitan and earlier), Apple's release of Java 6 comes pre-installed. If installed, it can be be found at this location:

/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home

Note that Java 6 passed its end-of-life long ago, so upgrading to a newer version is recommended. There is more information on reinstalling Apple Java 6 on the Oracle website.

Only Oracle JDKs and JREs are available for Windows platforms. The installation procedure is straight-forward:

1. Visit the Oracle Java Downloads page (opens new window):
2. Click on either the JDK button, the JRE button or the Server JRE button. Note that to develop using Java you need JDK. To know the difference between JDK and JRE, see here (opens new window)
3. Scroll down to the version you want to download. (Generally speaking, the most recent one is recommended.)
4. Select the "Accept License Agreement" radio button.
5. Download the Windows x86 (32 bit) or Windows x64 (64 bit) installer.
6. Run the installer ... in the normal way for your version of Windows.

An alternate way to install Java on Windows using the command prompt is to use Chocolately:

 C:\> choco install jdk8

Getting up and running with portable versions

There are instances where you might want to install JDK/JRE on a system with limited privileges like a VM or you might want to install and use multiple versions or architectures (x64/x86) of JDK/JRE. The steps remain same till the point you download the installer (.EXE). The steps after that are as follows (The steps are applicable for JDK/JRE 7 and above, for older versions they are slightly different in the names of folders and files):

This way, you can install any versions of JDK/JRE you need to be installed simultaneously.

Original post : http://stackoverflow.com/a/6571736/1448252 (opens new window)

There have been many releases of Java since the original Java 1.0 release in 1995. (Refer to Java version history (opens new window) for a summary.) However most releases have passed their official End Of Life dates. This means that the vendor (typically Oracle now) has ceased new development for the release, and no longer provides public / free patches for any bugs or security issues. (Private patch releases are typically available for people / organizations with a support contract; contact your vendor's sales office.)

In general, the recommended Java SE release for use will be the latest update for the latest public version. Currently, this means the latest available Java 8 release. Java 9 is due for public release in 2017. (Java 7 has passed its End Of Life and the last public release was in April 2015. Java 7 and earlier releases are not recommended.)

This recommendation applies for all new Java development, and anyone learning Java. It also applies to people who just want to run Java software provided by a third-party. Generally speaking, well-written Java code will work on a newer release of Java. (But check the software's release notes, and contact the author / supplier / vendor if you have doubts.)

If you are working on an older Java codebase, you would be advised to ensure that your code runs on the latest release of Java. Deciding when to start using the features of newer Java releases is more difficult, as this will impact your ability to support customers who are unable or unwilling their Java installation.

Java release naming is a little confusing. There are actually two systems of naming and numbering, as shown in this table:

^{1 - It appears that Oracle intends to break from their previous practice of using a "semantic version number" scheme in the Java version strings. It remains to be seen if they will follow through with this.}

The "SE" in the marketing names refers to Standard Edition. This is the base release for running Java on most laptops, PCs and servers (apart from Android).

There are two other official editions of Java: "Java ME" is the Micro Edition, and "Java EE" is the Enterprise Edition. The Android flavor of Java is also significantly different from Java SE. Java ME, Java EE and Android Java are outside of the scope of this Topic.

The full version number for a Java release looks like this:

1.8.0_101-b13

This says JDK 1.8.0, Update 101, Build #13. Oracle refers to this in the release notes as:

Java™ SE Development Kit 8, Update 101 (JDK 8u101)

The update number is important -- Oracle regularly issue updates to a major release with security patches, bug fixes and (in some cases) new features. The build number is usually irrelevant. Note that Java 8 and Java 1.8 refer to the same thing; Java 8 is just the "marketing" name for Java 1.8.

A JDK installation and a text editor are the bare minimum for Java development. (It is nice to have a text editor that can do Java syntax highlighting, but you can do without.)

However for serious development work it is recommended that you also use the following:

• A Java IDE such as Eclipse, Intellij IDEA or NetBeans
• A Java build tool such as Ant, Gradle or Maven
• A version control system for managing your code base (with appropriate backups, and off-site replication)
• Test tools and CI (continuous integration) tools

Using Alternatives

Many Linux distributions use the alternatives command for switching between different versions of a command. You can use this for switching between different versions of Java installed on a machine.

$ JDK=/Data/jdk1.8.0_67

 $ sudo alternatives --install /usr/bin/java java $JDK/bin/java 2
 $ sudo alternatives --install /usr/bin/javac javac $JDK/bin/javac 2
 $ sudo alternatives --install /usr/bin/jar jar $JDK/bin/jar 2

Now you can switch between different versions of a Java command as follows:

$ sudo alternatives --config javac

There is 1 program that provides 'javac'.

  Selection    Command
-----------------------------------------------
*+ 1           /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.101-1.b14.fc23.x86_64/bin/javac
   2           /Data/jdk1.8.0_67/bin/javac

Enter to keep the current selection[+], or type selection number: 2
$

For more information on using alternatives, refer to the alternatives(8) (opens new window) manual entry.

Arch based installs

Arch Linux based installs come with the command archlinux-java to switch java versions.

Listing installed environments

$ archlinux-java status
Available Java environments:
  java-7-openjdk (default)
  java-8-openjdk/jre

Switching current environment

# archlinux-java set <JAVA_ENV_NAME>

Eg:

# archlinux-java set java-8-openjdk/jre

More information can be found on the Arch Linux Wiki (opens new window)

After installing a Java SDK, it is advisable to check that it is ready to use. You can do this by running these two commands, using your normal user account:

$ java -version
$ javac -version

These commands print out the version information for the JRE and JDK (respectively) that are on your shell's command search path. Look for the JDK / JRE version string.

• If either of the above commands fails, saying "command not found", then the JRE or JDK is not on the search path at all; go to Configuring PATH directly below.
• If either of the above commands displays a different version string to what you were expecting, then either your search path or the "alternatives" system needs adjusting; go to Checking Alternatives
• If the correct version strings are displayed, you are nearly done; skip to Checking JAVA_HOME

Configuring PATH directly

If there is no java or javac on the search path at the moment, then the simple solution is to add it to your search path.

First, find where you installed Java; see Where was Java installed? below if you have doubts.

Next, assuming that bash is your command shell, use a text editor to add the following lines to the end of either ~/.bash_profile or ~/.bashrc (If you use Bash as your shell).

JAVA_HOME=<installation directory>
PATH=$JAVA_HOME/bin:$PATH

export JAVA_HOME
export PATH

... replacing <installation directory> with the pathname for your Java installation directory. Note that the above assumes that the installation directory contains a bin directory, and the bin directory contains the java and javac commands that you are trying to use.

Next, source the file that you just edited, so that the environment variables for your current shell are updated.

$ source ~/.bash_profile

Next, repeat the java and javac version checks. If there are still problems, use which java and which javac to verify that you have updates the environment variables correctly.

Finally, logout and login again so that the updated environment variables ptopagate to all of your shells. You should now be done.

Checking Alternatives

If java -version or javac -version worked but gave an unexpected version number, you need to check where the commands are coming from. Use which and ls -l to find this out as follows:

$ ls -l `which java`

If the output looks like this, :

lrwxrwxrwx. 1 root root 22 Jul 30 22:18 /usr/bin/java -> /etc/alternatives/java

then the alternatives version switching is being used. You needs to decide whether to continue using it, or simply override it by setting the PATH directly.

• Configuring and Switching Java versions on Linux using alternatives (opens new window)
• See "Configuring PATH directly" above.

Where was Java installed?

Java can be installed in a variety of places, depending on the installation method.

• The Oracle RPMs put the Java installation in "/usr/java".
• On Fedora, the default location is "/usr/lib/jvm".
• If Java was installed by hand from ZIP or JAR files, the installation could be anywhere.

If you are having difficultly finding the installation directory, We suggest that you use find (or slocate) to find the command. For example:

$ find / -name java -type f 2> /dev/null

This gives you the pathnames for all files called java on your system. (The redirection of standard error to "/dev/null" suppresses messages about files and directories that you can't access.)

Follow the below steps to install Oracle JDK from the latest tar file:

sudo su

mkdir /opt/jdk

tar -zxf jdk-8u5-linux-x64.tar.gz -C /opt/jdk

ls /opt/jdk

update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_05/bin/java 100

update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_05/bin/javac 100

Expected output:

java version "1.8.0_111"
Java(TM) SE Runtime Environment (build 1.8.0_111-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)