install java
lufei@lufei:~$ java
The program ‘java’ can be found in the following packages:
* default-jre
* gcj-5-jre-headless
* openjdk-8-jre-headless
* gcj-4.8-jre-headless
* gcj-4.9-jre-headless
* openjdk-9-jre-headless
`sudo apt install openjdk-9-jdk`$ sudo apt-key adv –fetch-keys http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1604/x86_64/7fa2af80.pub
Executing: /tmp/tmp.gV2Vh9azBW/gpg.1.sh –fetch-keys
http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1604/x86_64/7fa2af80.pub
gpgkeys: no key data found for http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1604/x86_64/7fa2af80.pub
gpg: no valid OpenPGP data found.
gpg: Total number processed: 0
gpg: keyserver communications error: key not found
gpg: keyserver communications error: bad public key
gpg: WARNING: unable to fetch URI http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1604/x86_64/7fa2af80.pub: bad public key”
Refer [SO](https://askubuntu.com/questions/769467) to solve it
`sudo apt-get -o Dpkg::Options::="--force-overwrite" install openjdk-9-jdk`
then your can check your java version with
` java -version`openjdk version “9-internal”
OpenJDK Runtime Environment (build 9-internal+0-2016-04-14-195246.buildd.src)
OpenJDK 64-Bit Server VM (build 9-internal+0-2016-04-14-195246.buildd.src, mixed mode)
“`