I had some questions while studying and teaching JAVA for a long time. Abstract classes and interfaces seem similar, so is it really necessary to separate them? It is convenient to use static, but why not treat all variables and methods like that? Most of the parts that I did not know exactly conceptually were resolved through this lecture. If you are learning the basics of Java or have completed learning and are still unclear about the concepts, I think you will be able to resolve your questions through this lecture. I think it was a very effective lecture with examples and explanations.