C Language is very hard and much more powerful then both C++ and Java.
It is used in very high programing companies like Microsoft, Oracle, IBM, etc.
C++ belongs to Microsoft the latest version is Visual Studio 2012 (including basic, C#, etc)
It is being replace by C # (C Sharp) it is Microsoft Operating System dependable, meaning you must have MS DOS for C++ and MS Wimdows for Visual C++ to run the program.
Java belongs to SUN System and Oracle Corporation.
It is platform free meaning it does not need any operating system, it is text based, so you can write the program in a notepad and connect it to the javavw to run it.
It is free, there are many versions of Java and Java Compilers, many software applications are there which help you to write codes and execute Java programs (i.e Eclipse)
Note: About 90% of the programs you work on are written in C language, both C++ and Java are written in C Language.
if you known anyone of these C++, Java, Pascal, Basic, Deplhi, etc
you already know the other they all use the same syntax just different libraries and begin and end commands.