# What is Java?

Java is a concurrent, class-based, object-oriented language specifically designed to have as few implementation dependencies as possible. It is intended to allow application developers to "write once, run anywhere", meaning that code that runs on one platform does not need to be recompiled to run on another.

Java is a registered trademark of Oracle and/or its affiliates.

> [wikipedia.org/wiki/Java_(programming_language)](http://en.wikipedia.org/wiki/Java_%28programming_language%29)

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# How to use this image

## Start a Java instance in your app

The most straightforward way to use this image is to use a Java container as both the build and runtime environment. In your `Dockerfile`, writing something along the lines of the following will compile and run your project:

```dockerfile
FROM java:7
COPY . /usr/src/myapp
WORKDIR /usr/src/myapp
RUN javac Main.java
CMD ["java", "Main"]
```

You can then run and build the Docker image:

```console
$ docker build -t my-java-app .
$ docker run -it --rm --name my-running-app my-java-app
```

## Compile your app inside the Docker container

There may be occasions where it is not appropriate to run your app inside a container. To compile, but not run your app inside the Docker instance, you can write something like:

```console
$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp java:7 javac Main.java
```

This will add your current directory as a volume to the container, set the working directory to the volume, and run the command `javac Main.java` which will tell Java to compile the code in `Main.java` and output the Java class file to `Main.class`.

# Why is this only OpenJDK/OpenJRE?

As all of the major upstream Linux distributions are unwilling to redistribute Oracle Java in their own distribution channels, we have chosen to follow them. See references below on how each distribution does not distribute Oracle Java.

-	Ubuntu stopped distributing it in the `sun-java6` package when Oracle retired the "Operating System Distributor License for Java" ([lists.ubuntu.com](https://lists.ubuntu.com/archives/ubuntu-security-announce/2011-December/001528.html)).
-	Debian requires users to download the Java tar manually from oracle.com and then use `java-package` to install it ([wiki.debian.net](https://wiki.debian.org/Java/Sun)).
-	The webupd8 PPA for Ubuntu and Debian requires the user to accept the Oracle license in order for their software to download and install Oracle java ([webupd8.org](http://www.webupd8.org/2012/09/install-oracle-java-8-in-ubuntu-via-ppa.html)).
-	Gentoo has a *fetch-restriction* that requires the user to go to the Oracle website to download the Java tar manually which inclues accepting the license ([wiki.gentoo.org](https://wiki.gentoo.org/wiki/Java)).
-	CentOS requires users to go and download the rpm provided by Oracle at java.com and thus accept the Oracle license ([wiki.centos.org](https://wiki.centos.org/HowTos/JavaRuntimeEnvironment)).
-	RedHat provides instructions to add a repo that is maintained by Oracle ([access.redhat.com](https://access.redhat.com/solutions/732883)).