• In a command line program, no. Java will run about as fast as a C or C++ program. It's when you start to add in graphical pieces that you see C languages shine, especially C#, since it can do any JIT optimization that Java can do, but it can bring it down to Assembly, if needed. Furthermore, any advanced graphics, such as some form of 3D graphics (DIrectX, OpenGL, which he said he was interested in), will blow Java away in terms of an equivalent implementation. Compare Minecraft's (Java) memory and CPU footprint to even a semi-modern game, and you'll see the difference. My laptop can run HL2 with little difficulty, but can't run any "full-fledged" Java 3D game well at are. Using Minecraft as an example, I can't render past the "very-near" setting without massive lag. Stuff
  
• I don't consider a wall of text to be good documentation. Compare Java documentation to the PHP documentation (which is complete with user comments), or even the MSDN documentation for any Visual Studio language. Everything is neatly organized so that you see only what you wish to see, instead of having to crawl through a mile of tables to find what you want.
  
• Yes, but it's also good to not make these mistakes in the first place. Learning good fundamentals about security is better than relying on a language to do it for you.
  
• Auto garbage collection will never compare to a tailored garbage collector, such as a combination of Smart Pointers and Memory Pools, among the many other advanced techniques unavailable to Java.
  
• Cross platform is not a good reason to choose a language, especially performance critical programs. The only exception I would have to this would be an enterprise-level program, however, in this case, an internal program would usually be run on the same system throughout the company. A commercial application is a different story.
  
• Java 7*. Typo.
  

That's kinda why I suggested it. I feel that design is important regardless of the scope of the project, and what someone will take from waterfall is to do design before coding.

If you tell someone to do any methodology, they'll most likely just take the main focuses of it: "XP" will mean pair programming and TDD, "Scrum" will mean sprints and stand-ups, "RAD" will mean use a bunch of auto-generating software, etc. Apparently a lot of businesses that say they are running under a specific methodology really aren't.

Anyway, if you really are interested in involving coding in your profession, you need to understand design. If you're just learning to make fun little programs, it's not as important. On that note, Java dominates the Android market, and Objective-C dominates the iPhone market.