Java and C are both C-syntax languages with curly braces, semicolons, and similar methods of variable and pointer declaration (kinda). They both have a long history of use in enterprise software. They both allow for pretty low-level operations depending on what frameworks/packages you're running with. If you can read C/C++, it's usually pretty easy to follow along with Java. The reverse isn't always true.
The biggest difference is that C runs on bare metal and Java runs in a VM. When you compile C to bytecode, that bytecode can be run directly by your processor. When you compile Java, that bytecode is run by an intermediate program called the Java Virtual Machine. This means that Java is a bit slower than C, but still extremely fast compared to interpreted languages like Python. It also means that you can't use Java as a systems language, e.g. you can't write an operating system in it.
Of course, there are tons of other differences and either language would take years of dedicated effort to truly master. If you have more specific questions I can elaborate further :)
thanks