Re: How to separate interface from implementation when using JARs?

Patrick May <>
Mon, 17 Sep 2007 13:24:22 -0400
Marc <> writes:

 In an engineering world where I used to be working with C++ I am
 now shiftnig to Java. In C++ I would publishe my interfaces in
 header files. In Java I can use the interface concept. However
 this is not sufficient for me. I want to be able to full separate
 the implementation from the interface of e.g. a class method.


 public interface MyMath {
int MyAdd(int a, int n);

class Calculate implements MyMath {
int MyAdd(int a, int n) {
return a - b;

I would use this class as an import in my client code:

#import Calculate

class client {
void DoIt() {
Calculate c = new Calculate();
int sum = c.MyAdd(9,7);

Once I discover the implementation error in the Calculate and want
to fix that I do not want to change the client code to require
recompilation/distribution. In C++ I would not have to change the
header file,only a cpp file. I would compile and link the math
library to a dll and redistribute only that DLL. In basic JAVA, when
I recompile my client code will recompile leading to a new
(changed?) client JAR which I should also redistibute. This is
undesired for me.

     If I understand your issue correctly, you can achieve something
similar by creating separate jar files for interfaces and
implementations. With that approach, you could release only the
implementation jar when fixing a bug.

     If you have a distributed system, you could dynamically download
updates by distributing jars only to class servers. One Java
technology that supports this is Jini (



S P Engineering, Inc. | Large scale, mission-critical, distributed OO
                       | systems design and implementation.
 | (C++, Java, Common Lisp, Jini, middleware, SOA)

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