I came from C++ and started learning Java for the first time and took this course. I thought that Ioc was just managing the creation and destruction cycle of classes that needed singletons to compensate for the destruction of objects, which is one of the shortcomings of the existing singleton pattern, but I found out that it also controls other life cycles in addition to singletons. There were many other things that I went through, but I think it's not enough to just go through it once.