Recently java 9 has been released and support to make your eclipse IDE ready to build, debug and run Java 9 code. Java 9 applications are available at Eclipse Marketeplace and you may install it from Marketeplace client in the Eclipse IDE by going to Help-> Eclipse Marketeplace or by dragging and dropping the following button onto your running Eclipse IDE.
Update your eclipse to Oxygen(4.7 or above) eclipse SDK or install latest eclipse Oxygen
Download JDK 9 available on oracle website. Find the link from here
Install JREs in your project by adding JRE defiinition in your project or by following the steps given below.
Go to Windows->Preferences->Java->Installed JREs->Add
Provide jdk 9 path
Create java project and manually select jdk 9 from the drop down list.
Find the video below which demonstrate a step wise procedure.
Note: if you are facing issues like jdk is not on correct path.. Simply update your eclipse and try the procedure again.
Here is the video link of Java 9 Support for Eclipse IDE and 1st Java 9 Example