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Java Forum / General / December 2006Does Javac converts class into .h files
What does Javac does to a Java Class? I heard it generates .h files Does it convert Java Program into a C Program Any help will be expected. I am considering converting a Java Program into C Program to increase its efficiency. Bye Sanny > What does Javac does to a Java Class? I heard it generates .h files Javac is the standard Java compiler. It converts source files (.java) into class files (.class). Are you confusing it with javah, which generates C header files for classes with native methods? Dan.  SignatureDaniel Dyer http://www.dandyer.co.uk > What does Javac does to a Java Class? I heard it generates .h files You have now started three separate threads based around converting your Java into ..an exe or C++ or whatever, based on the misunderstanding that it will become faster. Thus far, you have resisted my attempts to further analyse your applet so I might make recommendations. Basically - I am not convinced that - writing this applet in any other language will (necessarily) make it run faster. - the applet code is as fast as it might be. Perhaps you should be investigating why the code is so 'slow', before rushing off to other langauges or launch methods. So I repeat - what is an URL for the applet? Andrew T. > > What does ... ... > So I repeat - what is an URL for the applet? E.G. is this the mess you are referring to? <LOUD sounds warning> http://www.getclub.com/Chess.html </LOUD sounds warning> That is one horrendously broken piece of (D)HTML. The page seems to be doing continual (and very irritating) fetches. The entire page needs to be validated, and the scripts externalised and debugged. The class file is not in a jar file (which compresses it and speeds download time). The music (whatever it is) should be included as a separate resource (or even better still, not included at all) and played only on request - who wants to listen to crappy, (through most soundcards) music while playing *chess* anyway?! ..Is that what that applet is for? I had refused the 'give a nickname' crap and ended at some default screen, so it was impossible to go further. I can tell you this though. If your HTML and JS skills are indicative of your ability to write Java and C/C++, a) the applet is slow because of the code b) writing it in another language will result in another binary - that will also run slow. Andrew T. > What does Javac does to a Java Class? I heard it generates .h files > > Does it convert Java Program into a C Program Any help will be > expected. It seems you are intermixing several different things: (1) The java-compiler javac (not javah) produces a Java class file (*.class) from java source file (*.java) (2) javah produces a C header file (*.h) from a from Java class file. It does not generate any executable C code. It generates only C declarations, which will be the interface between Java code (in *.class file, generated by the javac compiler) and C code (in *.c files, to be hand-written by you). > I am considering converting a Java Program into C Program to > increase its efficiency. > > Bye > Sanny SignatureThomas > (2) javah produces a C header file (*.h) from a from Java class file. > It does not generate any executable C code. It generates only C > declarations, which will be the interface between Java code (in *.class > file, generated by the javac compiler) and C code (in *.c files, to be > hand-written by you). Ok javah creates .h file for the Applet. Then how can I use .C files So that Applet Calls .c files to compute time intensive calculations. Could it be done. Say I have a Java class ABC.class with 3 functions I create ABC.h file for that class. Now I create ABC.c file which implements the three functions. Now I want to utilize functions in ABC.c So how will I make a call to C files created from the Java Applet ABC.class Bye Sanny >> (2) javah produces a C header file (*.h) from a from Java class file. >> It does not generate any executable C code. It generates only C [quoted text clipped - 18 lines] > Bye > Sanny This sounds like a bad idea. Firstly, applets aren't really intended to have native methods. Although it can be achieved with a signed applet, it isn't sensible because you have no idea what platform the user is going to be using. If you build an applet that runs only on Windows, I can't use it on my Mac or Linux machines. And even if I am using Windows, I'd have to be stupid to grant you the necessary privileges to get the code to run. Secondly, despite the myths, using JNI rarely improves performance significantly (there are exceptions), it often makes it worse. There was an article on java.net the other day about this (http://weblogs.java.net/blog/mlam/archive/2006/12/beware_of_the_n.html). You should address the issues that Andrew raised in his response before going down this route. Dan. SignatureDaniel Dyer http://www.dandyer.co.uk > Secondly, despite the myths, using JNI rarely improves performance > significantly (there are exceptions), it often makes it worse. There was [quoted text clipped - 3 lines] > You should address the issues that Andrew raised in his response before > going down this route. Thanks for your sincere help. Bye Sanny [...] > I am considering converting a Java Program into C Program to > increase its efficiency. Don't expect too much from this approach! Making a Java program more efficient very rarely needs developing new C code (with javah & JNI). (1) Usually the time-consumption of a Java program is concentrated around a few hot-spots instead of being uniformly distributed. Be sure to spot these performance bottle-necks by *testing* (with some kind of profiler tool) instead of by *reasoning*. Guessing the bottle-necks only by intuition is almost always (in my experience) wrong. (2) Tuning the performance in most cases (in my experience) can be achieved by optimizing the design of your Java code. There is rarely need for replacing Java code by native C code. (3) Be aware that there is already a huge amount of native C code (native DLLs in Sun's JRE) working behind the scenes. For example for file I/O, network I/O, uncompressing jar/zip/jpeg/gif files, painting on screen, playing sound, .... SignatureThomas <snip> All good explanations, but just wanted to requote this part.. > ....Be sure to spot these > performance bottle-necks by *testing* (with some kind of profiler tool) > instead of by *reasoning*. Guessing the bottle-necks only by intuition is > almost always (in my experience) wrong. That is perhaps the best advice that has yet come out of this thread(s). Andrew T. > (1) Usually the time-consumption of a Java program is concentrated around a > few hot-spots instead of being uniformly distributed. Be sure to spot these > performance bottle-necks by *testing* (with some kind of profiler tool) > instead of by *reasoning*. Guessing the bottle-necks only by intuition is What are profiler tools How to get them and use. Bye Sanny >> (1) Usually the time-consumption of a Java program is concentrated around a >> few hot-spots instead of being uniformly distributed. Be sure to spot these >> performance bottle-necks by *testing* (with some kind of profiler tool) >> instead of by *reasoning*. Guessing the bottle-necks only by intuition is > > What are profiler tools How to get them and use. See for example <http://mindprod.com/jgloss/profiler.html> SignatureThomas Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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