WSL（Windows Subsystem for Linux ）的環境變量是包含Linux子系統和Windows系統的，測試如下：

wy@WY-PC:/mnt/c/Windows/System32$ python -V
Python 2.7.12
wy@WY-PC:/mnt/c/Windows/System32$ python.exe -V
Python 2.7.14
wy@WY-PC:/mnt/c/Windows/System32$ python3 -V
Python 3.5.2
wy@WY-PC:/mnt/c/Windows/System32$ python3.exe -V
Python 3.6.3
 

wy@WY-PC:/mnt/c/Windows/System32$ java -version
程序 ‘java‘ 已包含在下列軟件包中：
 * default-jre
 * gcj-5-jre-headless
 * openjdk-8-jre-headless
 * gcj-4.8-jre-headless
 * gcj-4.9-jre-headless
 * openjdk-9-jre-headless
請嘗試：sudo apt install <選定的軟件包>
wy@WY-PC:/mnt/c/Windows/System32$ java.exe -version
java version 
 
"1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b18)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)
wy@WY-PC:/mnt/c/Windows/System32$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/mnt/d/Program Files/Java/jdk1.8.0_25/bin:/mnt/d/Program Files/Java/jdk1.8
 
.0_25/jre/bin:/mnt/c/Windows/System32:/mnt/c/Windows:/mnt/c/Windows/System32/wbem:/mnt/c/Windows/System32/WindowsPowerShell/v1.0:/mnt/c/Program Files (x86)/NVIDIA Corporation/PhysX/Common:/mnt/e/Android/sdk/platform-tools:/mnt/e/Android/sdk/tools:/mnt/c/Users/wy/AppData/Local/Programs/Python/Python36/Scripts:/mnt/c/Users/wy/AppData/Local/Programs/Python/Python36:/mnt/c/Users/wy/AppData/Local/Microsoft/WindowsApps:/mnt/d/Program Files/Java/jdk1.8.0_25/jre/bin:/mnt/c/Windows/System32:/mnt/c/Windows:/mnt/c/Windows/System32/wbem:/mnt/c/Windows/System32/WindowsPowerShell/v1.0:/mnt/c/Program Files (x86)/NVIDIA Corporation/PhysX/Common:/mnt/e/Android/sdk/platform-tools:/mnt/c/Python27/Scripts:/mnt/c/Python27
wy@WY-PC:/mnt/c/Windows/System32$

Windows Subsystem for Linux 環境變量