I have Windows 10 and Java is already installed in my system. But I have eclipse Luna with only CDT installed on it, but doesn't have JDT. Do I have to download java once more for installing it on eclipse or can I just give the path to JRE and write a java program. If yes, How to do it?
Yes you need to install JDT (java development tools) related plug ins but not Java.
You can check what is already installed through Help ->Check for Updates-> What is already installed. If you don't see JDT, please then install JDT.
cheers,
Saurav