Java is harder because ...

• Java is more powerful and can do much more than C. For example, C doesn't have a graphical user interface (GUI), and C doesn't have any way to do object-oriented programming (OOP). It's possible to write in Java in a C style, avoiding the new powerful features of Java. But that is foolish.
• Java either checks for errors, or makes you check for errors. C lets you do many things that would cause errors (for example, convert strings to integers, or do I/O), but doesn't make you write code to handle the errors. Java makes you write try...catch statements around things that might cause problems.