Best way to learn Java in easy way

what should I know before learning Java

Well, it doesnt really matter at all , if youre interested enough you can directly give it a start with java . However having a prior knowledge of basic OOPs concepts and a little programming experience(or basic programming concepts) would help you to understand it better and make it easier . Though not mandatory , but to have a strong grip over the concepts before switching to java you can go with C/ C++ ( suggesting as I started with C++ and it has helped me a lot to understand java better)

I am also a java learner but i would like to answer your question. Here all important tips are already given but i want to add only one more point which is much important.
If you are a beginner, please don't use any kind of IDE.
IDE is specially made for those who already a pretty decent experienced in programming.
It is helpful for them who are in a very big project development. I would recommend to use notepad and command prompt as a beginner.
As using this you have nothing to help you except the internet articles.
So you can rectify your error yourself. In this way you have gain also a decent experience while learning.
This learning method is slow but very effective.
Although you have to use IDE in your future but you will have a good ability to rectify your mistakes.
You can gain a good idea of what type error comes for what kind of mistakes.

Conclusion

I hope you found this article useful, if you need any help please let me know in the comment section.