A few days ago I installed Oracle JDK 9. I tried to use Eclipse, but it didn\'t work. I looked around and found this link. So I updated my Eclipse with the link showed after
As also confirmed in the comments, the issue is filed as BUG#525711 in Eclipse.
Update:- It has been verified as fixed in M20171115-1700, which primarily means that if one is using nightly or builds released after November 15, 2017 they should be able to create JAR using Eclipse.
=> Though another point to note here shall be that this causes a subsequent BUG#527114 for failure in handling multiple modules while creating the JAR.
I would guess one shall mostly expect these updated in the Eclipse Photon build in future.