Shift from Java to c++_问答_开发者_运维开发者技术经验分享

I have been developing applications based on C# (.net) and Java (J2EE) for the last 3 years.

But now I feel, Java, C# makes you lame (from learning point of view) and you can develop your apps quickly but you fail to understand the basic underlying concepts of programming.

So, I am trying to learn C++, but I find it a little "confusing" due to pointer, multiple inheritance, some conventions and other concepts of C++ which don't exi开发者_开发百科st in Java. So, what do you guys suggest? How should I feel about it?

Thanks

PS: I am a student, so have all the time in the world and actually shift.

In my opinion, you should learn C first in order to properly understand the base upon which C++ is built. Pick up a copy of "The C Programming Language" by Kernighan and Ritchie, widely considered the best reference on the language, and start reading through it. Once you fully understand C, you'll have the low-level base you need.

C++ is no more "basic and underlying" than any other modern programming language. It has a model of a computer (a flat memory address space), but the OS and CPU merely simulates that model using many layers of caching and paging, so it's not "real". The result is that the same operation may sometimes take 1000s of times longer to complete than at other times.

Also modern C++ has lots of powerful abstractions that have no more direct relationship with how a computer works than do the abstractions provided in Java and C#. The OP mentions multiple inheritance - clearly no more elemental than inheritance in other OO languages. Many other features of C++ omitted from Java are high-level abstractions (or allow you to build them) and so in some ways Java is the more low-level language. In Java the meaning of operator symbols is always the same, whereas in C++ a simple == might build an object that will later be used to generate a SQL expression instead of being executed in-process.

The JVM and CLR runtimes are (almost certainly) written in C and/or C++, so in that sense obviously they happen to form layers today. But at the C/C++ layer you will still be working in an abstraction that is not "how the machine really works", so you'll really just be learning a different set of abstractions, rather than "reality". And an OS (or indeed a hardware chip) can be designed specifically so that JVM or CLR like runtimes are the native low-level layer of the system; on such a system it would be the C/C++ runtime that would require a "high-level" (expensive) emulation layer in order to work.

So it is probably not worth trying to learn how to program in "reality". No one really does that these days; it's a waste of time. You're better off learning about how programming abstractions help you to write correct programs. If a language makes life difficult for you, that doesn't prove you're doing the "real thing". It just means you picked the wrong language for what you're trying to do.

I disagree with the sentiment that you need to learn C or assembly language first. C++ and C may be similar in theory but are very different in terms of practical use. One gains little to nothing in the way of C++ idioms by using only C, and while it is good to have practical experience in multiple languages, it's an exercise in futility to specify prerequisites in language learning. I think the best way to learn the concepts of programming is to sit down with someone who understands them well and just talk about it, be that on StackOverflow, in forums, or, if you're lucky, in person.

At the end of the day, I think programming really isn't all that hard, and you may need someone to explain it right just one time to have everything click. It's all about rehashing the same simple concepts over and over to build complex and beautiful machines.

For learning c++ I reccommend reading C++ for Java Programmers by Mark Allen Weiss. It helped me alot when moving from Java to C++ as it is very good at highlighting the differences between the languages.

But, now I feel, Java, C# makes you lame (from learning point of view) and you can develop your apps quickly but you fail to understand the basic underlying concepts of programming.

If you're trying to learn the concepts of programming, rather than machine architecture, there's not much benefit to learning C++. I would suggest going with something different from Java all together. A Lisp variant, perhaps.

How To Design Programs is a pretty good book.

If you want to understand the underlying concepts of programming languages, I would suggest a book such as John Mitchell's Concepts in Programming Languages. Follow this up by writing a few parsers/interpreters for simple languages. Another good resources is SICP, which is specific to Scheme (a LISP dialect), and available in full here. Once you've learned a few languages, it doesn't take too long to pick up the syntax and semantics of a new one (the core libraries on the other hand, can take quite a while to be familiarized with).

If you want to learn about how today's computers work, I'd recommend learning C and reading books such as Tanenbaum's Modern Operating Systems. C is useful in this context mostly for reading systems level code. Implementing a (very) simple operating system can be incredibly educational. However, something as simple as implementing a basic shell (like bourne shell, except simpler) is probably a better place to start. I'd also recommend learning about how networking works specifically, since it's such an integral part of modern computer systems.

C and C++ make some basic underlying programming concepts more evident, but they weren't designed by God. I'd second the suggestion to study the actual low-level systems behind your low-level code: operating systems, compilers/runtimes (try "Essentials of Programming Languages"), and machine architecture.

P.S. In general it may be better to study C++ on its own, rather than starting with C, but for your particular purpose -- getting more intimate with low-level, unsafe constructs such as pointers, after already learning Java -- I think it's better to start with C (and K&R) where these are front and center.

I would suggest learning assembly language first. This will give you a very solid foundation in what is happening at a low level. This will also help to reinforce the idea that "everything is really just an address".

Taking a class which focuses on assembly language is advisable since it will "force" you to learn it (personally, I don't think ASM is /that/ fun, but it was worthwhile [and a requirement for graduation] for me to take the class).

After you know assembly, go on to C and C++.

Have a lot of fun!

It sounds like you're avoiding the first mistake most people make, which is assuming the new language is the same as the old one. C++ is different and should be learned as a neww(-ish) language.
A reference I would suggest would be C++ How to Program which is used at my University for the introductory C++ classes.

After that, then look at previous Java software that you have written and seeing how you would translate them to C++. The syntax can easily be referenced from CPlusPlus.com. While doing this, it is important to keep in mind what all the different syntax represents, and how it changes what is going on in the software (i.e. The differences between the two languages). This has the added benefit of allowing you to see how the underlying architecture is represented for both languages (and for programming languages in general). I don't know of a good book that explains how programming languages work under the covers, or I'd recommend that.

If you are, however, interested in learning how programming works, then Assembly language would be a good place to start. Assembly language for Intel-Based Computers is what I used to learn assembly language and it was very useful.

Assembly Language.

Start with the Z-80. Then add 'x86. Then try 68000. Then the TI 320 series of DSP. You might also wish to add the Z-8. Just to see how different machines do it.

If you really want to know more about low level programming I would recommend learning C and Assembly. C++ is much more complex than C but really doesn't give you much more insight into low level concerns. It might be interesting if you want to learn about what type of concepts and constructs a programming language can be made up of though, since C++ has a lot of them.

There is also a lower level of your VM you don't seem to know yet and which you might want to explore. To learn about the internals of Java I would recommend learning how to program the JVM in (Java) Assembly language. Jasmin (http://jasmin.sourceforge.net/) is the reference assembler/syntax for this kind of programming. Another great resource is the Java Language specification (http://java.sun.com/docs/books/jls/third_edition/html/j3TOC.html) which contains a lot of Java internals. When you have learned C you can also use some lower level APIs the JVM provides (http://java.sun.com/javase/6/docs/technotes/guides/jvmti/) that allow you to retrieve low level information about a running JVM and write interesting things like debuggers.

If you learn this stuff and do some hacking on your own you will learn how the JVM works and what the compiler actually puts into your class files. It's also very likely that you discover some new things about the Java programming language itself you didn't know before even if you think you know everything about it.

You can also program the .Net VM in assembly by the way.

I think you should start with C, but not as a necessary preamble for learning C++. Rather, for learning C. In other words, while you learn C put your efforts into learning the language, feeling the philosophy of the language and focusing on letting it sip into your skin. Be a good C programmer and you will be a good programmer, period. Not just a good C++ programmer -- this has nothing to do with learning C -- but a good programmer.

There's another reason for learning C first. It's easier than C++, much easier than C++, and it bridges well to C++ (in contrast to Java, which doesn't in all aspects but the most superficial object-oriented ones). I'm not talking about the syntax similarities: I'm talking about low-level programming. I'm talking about the concepts of pointers, which exist as themselves and in the form of iterators in C++. You can pass around functions in C, and you can pass around function objects in C++. C is fast to learn, and it will warm you up very effectively.

Learning C will also eliminate the fear of free functions some pure OO programmers tend to have. C++ is a hybrid language, and C truly is a subset of C++, not just by syntax but by philosophy as well.

Start by getting yourself the K&R book and drinking it through. You won't regret this.

Whatever you start off with, my suggestion would be dump the full fledged IDE's. Use good text editors (vim/emacs)

The learning curve is better when using text editors since everything needs to be written on your own. No prompts and no pre-written code.

You have all the best answers above, in anycase. :)

Ivar

Set up a performant C++ compiling environment such as Microsoft Visual C++ 2008 Express and go through all links in Bjarne Strousrup's The C++ Programming Language site, beginning with C++ Style and Technique FAQ. If you are experimented in any other language you don't need more :-)

Learn C and C++ at the same time, I'm talking from experience here. Very often I come across code that mixes C and C++, so it's better to know both and their differences. Pick up K&R for C (understand pointers, header files and manual memory allocation and cleaning...which are not used by Java!) and any decent C++ beginner book (I picked Prata, but whatever you are more comfortable with). Practice the same examples doing versions of C, C++ in a sequential fashion, object-oriented (OO) fashion, generic/template fashion etc. C++ has a larger standard library than C: templates, STL containers (no need for pointers, but you can do pointer fine tuning writing your own container), threads (since C++11). You can always use C if you have no choice (or Boost libraries), any C++ compiler will allow it.

If you come from Java you should already know OO concepts for C++, and, perhaps, some generic programming as in C++ templates. C++ is mistakenly regarded as an OO language, but it's more than that. BTW, objects are a dynamic concept (runtime), whereas templates are static (compilation time), so learn the language CONCEPTS, not just the syntax! Once you learn the concepts read Stroustrup's book (he created C++) to learn his philosophy for the best design rules for C++ code.

Learn the latest C++ standard (C++11) as it adds many new things to the language (auto, nullptr, threads, lambda functions, new containers, etc.). Last but not least, please use Doxygen in C/C++ the same way you used Javadoc....there is nothing worse than undocumented, unreadable code no matter what language you're using.

Learn Forth. It has better Objects. And it is a virtual machine. Unless you want a real machine see Green Arrays or Sandpiper/John Rible for that.

Free threaded interpreted versions are all over the 'net. For practice. When you understand it write your own Direct Threaded version. Or see Forth Inc and buy one for your machine or use their free windows version.

Java is a Forth/C hybrid so if you want to go Java you will have some of the stuff under your belt.

Education:

Starting Forth - Brodie Thinking Forth - Brodie

The second is excellent for any language because it is the best book on factoring I know. Free Versions of both on the net.

If you want to do a hardware/FPGA Forth Stack Machines: The New Wave by Koopman

All the above books are free on the 'net.