Ubuntu / Google Compute Engine / Google Cloud：安装JAVA JDK8 或者 JAVA JDK 9, Install Oracle Java 8 / 9 in Ubuntu 16.04, Linux Mint 18

1. Add the PPA.

Open terminal (Ctrl+Alt+T) and run the command:

sudo add-apt-repository ppa:webupd8team/java

Type in your password when it asks and hit Enter.

2. Update and install the installer script:

Run commands to update system package index and install Java installer script:

sudo apt update && sudo apt install oracle-java8-installer

安装Java 9的看这里： You may replace oracle-java8-installer with oracle-java9-installer to install Java 9. 

While the install process, you have to accept Java license to continue downloading & installing Java binaries.

3. Check the Java version

To check the Java version after installing the package, run command:

javac -version

4. Set Java environment variables

The PPA also contains a package to automatically set Java environment variables, just run command:

sudo apt install oracle-java8-set-default

安装Java 9的看这里：For Java 9, install the package oracle-java9-set-default instead.

Google Compute Engine 实例安装 Java JDK， 如果以上方法不行的话，就用下载包安装吧！

1. 官网下载 JAVA JDK 9 ： 选中 Accept License Agreement，点击下载 jdk-9.0.4_linux-x64_bin.tar.gz
2. 运行一下代码：

   tar -xvf ~/Downloads/jdk-9.0.4_linux-x64_bin.tar.gz
   sudo mkdir -p /usr/lib/jvm/jdk-9.0.4
   sudo mv jdk-9.0.4/* /usr/lib/jvm/jdk-9.0.4/
   sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jdk-9.0.4/bin/java" 1
   sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/jdk-9.0.4/bin/javac" 1
   sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jvm/jdk-9.0.4/bin/javaws" 1

3. 注意，后面的 1 是参数，不要删除
4. 编辑 Edit the system path in file /etc/profile 设着PATH全局变量

   sudo vi /etc/profile

   在末尾添加：

   JAVA_HOME=/usr/lib/jvm/jdk-9.0.4
   PATH=$PATH:$HOME/bin:$JAVA_HOME/bin
   export JAVA_HOME
   export PATH

   然后source一下：

   source /etc/profile

5. 执行下面代码，看是安装否成功：

   java -version

本文：Ubuntu：安装JAVA 8 或者 JAVA 9, Install Oracle Java 8 / 9 in Ubuntu 16.04, Linux Mint 18