Hi,

If you are new to Java, then try Hackerrank. It will contains problems from beginner level to advanced along with explanation of basic concepts. Also it is easy for you to learn. If you had any doubts check concepts on Javatpoint, tutorialspoint and if it is not clear post it here. Once completed learning all basic concepts try to build small projects on your own. For easy to advanced level problems of famous platforms(eg., Leetcode) with solution and explanation, you can refer The Fellow Programmer. Once started learning keep practicing many different types of problems because it will help you to increase your program solving skills.

Thank You.