Some Java ORB products offer proprietary solutions to this problem...

Odnośniki

Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.
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W życiu są obecne rozmaite problemy – w związkach międzyludzkich, w pracy, w życiu osobistym...
U02 Umie formułować i rozwiązywać proste problemy z wykorzystaniem K_U04 rachunku wektorowego, rachunku macierzowego, układów...
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dość przekonywająca, aczkolwiek zmienia całą kontrowersję w nie- zbyt interesujący problem metodologiczny...
Na cotygodniowej audiencji, kiedy to wezyr przyjmował najbliższych współpracowników, rozpatrywano najróżniejsze problemy...
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Tak oto podjęty przez nas problem dotyka szerokiego zagadnienia czynu...

Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.

For example, some implement what is called HTTP Tunneling, while others have their special firewall features.
This is too complex a topic to be covered in an appendix, but it is definitely something you should be aware of.
CORBA vs. RMI
You saw that one of the main CORBA features is RPC support, which allows your local objects to call methods in remote objects. Of course, there already is a native Java feature that does exactly the same thing: RMI (see Chapter 15). While RMI makes RPC possible between Java objects, CORBA makes RPC possible between objects implemented in any language. It’s a big difference.
However, RMI can be used to call services on remote, non-Java code. All you need is some kind of wrapper Java object around the non-Java code on the server side. The wrapper object connects externally to Java clients via RMI, and internally connects to the non-Java code using one of the techniques shown above, such as JNI or J/Direct.
This approach requires you to write a kind of integration layer, which is exactly what CORBA does for you, but then you don’t need a third-party ORB.
Summary
What you’ve seen in this appendix are the most common techniques to call non-Java code from a Java application. Each technique has its pros and cons, but currently the major problem is that not all of these features are available on all JVMs, so a Java program that Appendix A: Using Non-Java Code
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calls native methods on a specific platform might not work on a different platform with a different JVM.
Sun’s JNI is flexible, reasonably simple (although it requires a lot of control over the JVM
internals), powerful, and it’s available on most JVMs, but not all. Microsoft, at the time of this writing, does not support JNI, but offers J/Direct, a simple way to call Win32 DLL
functions, and RNI, which is designed for high-performance code but requires a good understanding of the JVM internals. Microsoft also offers its proprietary Java/COM
integration feature, which is powerful and makes Java an interesting language for writing COM servers and clients. J/Direct, RNI, and Java/COM integration are supported only by the Microsoft compiler and JVM.
Finally, we took a look at CORBA, which allows your Java objects to talk to other objects regardless of their physical location and implementation language. CORBA is different from the techniques above because it is not integrated with the Java language, but instead uses third-party integration technology and requires that you buy a third-party ORB. CORBA is an interesting and general solution, but it might not be the best approach if you just want to make calls into the operating system.
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Thinking in Java
www.BruceEckel.com
# $
B: Comparing C++
and Java
As a C++ programmer, you already have the basic idea of object-
oriented programming, and the syntax of Java no doubt looks familiar to
you. This makes sense since Java was derived from C++.
However, there are a surprising number of differences between C++ and Java. These differences are intended to be significant improvements, and if you understand the differences you’ll see why Java is such a beneficial programming language. This appendix takes you through the important features that distinguish Java from C++.
1. The biggest potential stumbling block is speed: interpreted Java runs in the range of 20
times slower than C. Nothing prevents the Java language from being compiled and there are just-in-time compilers appearing at this writing that offer significant speed-ups. It is not inconceivable that full native compilers will appear for the more popular platforms, but without those there are classes of problems that will be insoluble with Java because of the speed issue.
2. Java has both kinds of comments like C++ does.
3. Everything must be in a class. There are no global functions or global data. If you want the equivalent of globals, make static methods and static data within a class. There are no structs or enumerations or unions, only classes.
4. All method definitions are defined in the body of the class. Thus, in C++ it would look like all the functions are inlined, but they’re not (inlines are noted later).
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5. Class definitions are roughly the same form in Java as in C++, but there’s no closing semicolon. There are no class declarations of the form class foo, only class definitions.
class aType {
void aMethod( ) { /* method body */ }
}