[absmiths]

I know it's possible but I can't find any way to use a Java library from within Objective-C. For example, for all I can tell Acquisition is written in Objective-C, but utilizes many network components that are written in Java. How is this accomplished?

Say I have these classes in Java:

Code:
public class Manager
{
  public Bean getBean()
  {
    return new BeanImpl();
  }

  public static Manager getInstance()
  {
    return new Manager();
  }
}

public interface Bean
{
  // . . .
  void x();
}

public class BeanImpl implements Bean
{
 // . . .
  public void x()
  {
    // . . .
  }
}

How would I go about doing this in Objective-C:

Code:
  // This is ObjC pseudo-code
  Manager man = Manager.getInstance();
  Bean bean = man.getBean();
  bean.x();

This must be possible, but Apple doesn't have any documentation that I can find. Also, what is the overhead of this? Is there a load of boxing or marshalling going on?

And is the reverse possible? Can I send an ObjC object into Java and call methods on it?

I would like to avoid JNI if at all possible.

This is on Panther and I have all the developer tools installed, in case the info is there.

[Chuckit]

Courtesy of Cocoa Dev Central: The Java Bridge

[absmiths]

Originally posted by Chuckit:
Courtesy of Cocoa Dev Central: The Java Bridge

Thank you very much. I had never seen that site before, very useful.

[Geobunny]

Firstly, I apologise for dredging up such an old thread.

Secondly, I'm trying to do the reverse of what's in Cocoa Dev Central's web page: I need to access an Objective-C object from within my Java code. I've got a cocoa-java project and I need to call various CFM routines which can only be done via Obj-C if I've understood correctly (this bit works correctly in its own mini obj-c project).

What I'm trying as a test is the following:

Code:
testClass.m

@implementation testClass
-(void) testMethod
{
NSLog(@"test line printed\n");
}
@end

In my Java code, I want to create an instance of testClass and call testMethod. I was under the impression that the Java-ObjC bridge would allow me just to do

Code:
testClass myTestClass = new testClass();

but it moans at compile time saying "testClass" can't be found/resolved.

I'd be really grateful for any pointers as my project's presently sitting in front of a bloody big brick wall! Thanks.

[Chuckit]

Firstly, in both Java and Objective-C, class names should start with a capital letter.

Second, I believe this thread on CocoaDev covers the issue pretty well (though I'm not sure you'll really love the answers).

[Angus_D]

Use JNI.

[Geobunny]

Originally Posted by Angus_D

Use JNI.

Care to elaborate? Please?

[Angus_D]

Originally Posted by Geobunny

Care to elaborate? Please?

Java Native Interface. Docs at sun:
http://java.sun.com/j2se/1.4.2/docs/guide/jni/
http://java.sun.com/docs/books/tutorial/native1.1/

Sample code from Apple:
http://developer.apple.com/samplecod...JNISample.html
http://developer.apple.com/samplecod...ashScreen.html
http://developer.apple.com/samplecod...aLauncher.html

[sqonk]

Java can't see the obj-c methods but you can talk directly to your Obj-C objects by using NSKeyValueCoding

public void someJavaMethod(NSObject objcObject) {
objcObject.valueForKey("testMethod");
}

if you want to return a value you use valueForKey(), if you want to pass a value you use takeValueForKey() and do the following:

in Obj-C change the method to

- (void)setTestMethod: (NSString*)msg
{
NSLog(msg);
}

(note that the 'set' prefix is nessesary as takeValueForKey() looks for a setter method)

then in java call it:

public void someJavaMethod(NSObject objcObject) {
objcObject.takeValueForKey("this is a test message from java!", "testMethod");
}

Obviously this can be a bit cumbersome but if all you wanna do is call some of your existing code it can save some time.