Assessing the Java Native Interface

1. Adapter
SENG 609.04 Design Patterns
Winter, 2003
Presented by Ming Zhou, Guy Davis

2. Agenda
Intent & Motivation

Structure

Applicability

Consequences

Known Uses

Related Patterns

References

- Total 17 pages - 1

3. What is Adapter?
Change the interface of a

class into another interface
which is expected by the
client.
A.K.A. Wrapper

- Total 17 pages - 1

4. What is Adapter?
Change the interface of a

class into another interface
which is expected by the
client.
A.K.A. Wrapper

- Total 17 pages - 1

5. What is Adapter?
Change the interface of a

class into another interface
which is expected by the
client.
A.K.A. Wrapper

- Total 17 pages - 1

6. Motivation
- Total 17 pages - 1

7. Motivation
- Total 17 pages - 1

8. Motivation
- Total 17 pages - 1

9. Motivation
1 1
- Total 17 pages - 1

10. Structure (Class)
- Total 17 pages - 1

11. Structure (Object)
- Total 17 pages - 1

12. Applicability
- Total 17 pages - 1

13. Applicability
Use an existing class whose interface

does not match the requirement
- Total 17 pages - 1

14. Applicability
Use an existing class whose interface

does not match the requirement
Create a reusable class though the

interfaces are not necessary
compatible with callers
- Total 17 pages - 1

15. Applicability
Use an existing class whose interface

does not match the requirement
 Create a reusable class though the
interfaces are not necessary
compatible with callers
 Want to use several existing subclasses,
but it is impractical to subclass
everyone. (Object Adapter Only)
- Total 17 pages - 1

16. Class Adapter Pattern
Pros

Only 1 new object, no additional indirection

Less code required than the object Adapter

Can override Adaptee's behaviour as required

Cons

Requires sub-classing (tough for single

inheritance)
Less flexible than object Adapter

- Total 17 pages - 1

17. Object Adapter Pattern
Pros

More flexible than class Adapter

Doesn't require sub-classing to work

Adapter works with Adaptee and all of its

subclasses
Cons

Harder to override Adaptee behavior

Requires more code to implement

properly
- Total 17 pages - 1

18. Pluggable Adapters
implemented with abstract operations

- Total 17 pages - 1

19. Pluggable Adapters
implemented with delegate objects

- Total 17 pages - 1

20. Two-way Adapters
class PegAdapter: public SquarePeg,
class SquarePeg {
RoundPeg {
public:
void virtual squarePegOperation() public:
{ blah }
void virtual roundPegOperation() {
}
add some corners;
squarePegOperation();
class RoundPeg {
}
public:
void virtual squarePegOperation() {
void virtual roundPegOperation()
add some corners;
{ blah }
roundPegOperation();
}
}
}
- Total 17 pages - 1

21. Adapting Local Classes to RMI
Comparison:
 Increases reusability
of local class
 Improves performance
of local class
 Doesn't use Java
single parent by
subclassing (uses
composition)
- Total 17 pages - 1

22. Related Patterns
Adapter can be similar to the remote

form of Proxy. However, Proxy doesn't
change interfaces.
Decorator enhances another object

without changing its interface.
Bridge similar structure to Adapter,

but different intent. Separates
interface from implementation.
- Total 17 pages - 1

23. Conclusions
Allows collaboration between classes

with incompatible interfaces
Implemented in either class-based

(inheritance) or object-based
(composition & delegation) manner
Useful pattern which promotes reuse

and allows integration of diverse
software components
- Total 17 pages - 1

24. References
Becker, Dan. Design networked applications in RMI using the Adapter design

pattern. JavaWorld Magazine, May 1999. http://www.javaworld.com/javaworld/
jw-05-1999/jw-05-networked.html
Buschmann et al. A System of Patterns: Pattern-Oriented Software Architecture.

John Wiley and Sons. Chichester. 1996
Gamma et al. Design Patterns: Elements of Reusable Object-Oriented Software.

Addison-Wesley. Boston. 1995
Nguyen, D.X. Tutorial 10: Stacks and Queues: The Adapter Pattern. Rice

University. 1999. http://www.owlnet.rice.edu/~comp212/99-fall/tutorials/10/
tutorial10.html
Whitney, Roger. CS 635 Advanced Object-Oriented Design & Programming. San

Diego State University. 2001. http://www.eli.sdsu.edu/courses/spring01/cs635/
notes/proxy/proxy.html#Heading10
Shalloway, Alan., and Trott, James R., Design Patterns Explained: A New

Perspective on Object-Oriented Design, Addison-Wesley, 2002.
Rising, Linda., The Patterns Handbook: Techniques, Strategies, and Applications,

Cambridge university Press, 1998.
- Total 17 pages - 1

25. Questions?
- Total 17 pages - 1

26. Questions?
- Total 17 pages - 1

27. Java Native Interface (JNI)
SENG 609.04 Design Patterns
Winter, 2003
Presented by Guy Davis, Ming Zhou

28. Agenda
Overview

Justification

Hello World!

Summary

References

Q&A

- Total 17 pages - 1

29. JNI Overview
- Total 17 pages - 1

30. Interactions with Native Code
Access to Java world from native code
Access to- native code from Java
Total 17 pages - 1

31. Justification
Pros:
 Reuse: allows access to useful native code
 Efficiency: use best language for the task
Cons:
 Applets: doesn't work as they're mobile
 Portability: native methods aren't portable
 Extra work: javah, create shared native libs
- Total 17 pages - 1

32. HelloWorld.java
class HelloWorld {
public native void displayHelloWorld();
static {
System.loadLibrary(quot;helloquot;);
}
public static void main(String[] args) {
new
HelloWorld().displayHelloWorld();
}
}
- Total 17 pages - 1

33. HelloWorld.java
class HelloWorld {
public native void displayHelloWorld();
static {
System.loadLibrary(quot;helloquot;);
}
public static void main(String[] args) {
new
HelloWorld().displayHelloWorld();
}
}
- Total 17 pages - 1

34. HelloWorld.java
class HelloWorld {
public native void displayHelloWorld();
static {
System.loadLibrary(quot;helloquot;);
}
public static void main(String[] args) {
new
HelloWorld().displayHelloWorld();
}
}
- Total 17 pages - 1

35. HelloWorld.java
class HelloWorld {
public native void displayHelloWorld();
static {
System.loadLibrary(quot;helloquot;);
}
public static void main(String[] args) {
new
HelloWorld().displayHelloWorld();
}
}
- Total 17 pages - 1

36. HelloWorld.h
#include “jni.h”
/* Header for class HelloWorld */
#ifndef _Included_HelloWorld
#define _Included_HelloWorld
#ifdef __cplusplus
extern “C” {
#endif
/*
* Class: HelloWorld
* Method: displayHelloWorld
* Signature: ()V
*/
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
- Total 17 pages - 1

37. HelloWorld.h
#include “jni.h”
/* Header for class HelloWorld */
#ifndef _Included_HelloWorld
#define _Included_HelloWorld
#ifdef __cplusplus
extern “C” {
#endif
/*
* Class: HelloWorld
* Method: displayHelloWorld
* Signature: ()V
*/
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
- Total 17 pages - 1

38. HelloWorld.h
#include “jni.h”
/* Header for class HelloWorld */
#ifndef _Included_HelloWorld
#define _Included_HelloWorld
#ifdef __cplusplus
extern “C” {
#endif
/*
* Class: HelloWorld
* Method: displayHelloWorld
* Signature: ()V
*/
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
- Total 17 pages - 1

39. HelloWorldImp.c
#include <jni.h>
#include quot;HelloWorld.hquot;
#include <stdio.h>
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *env, jobject obj)
{
printf(quot;Hello world!nquot;);
return;
}
- Total 17 pages - 1

40. HelloWorldImp.c
#include <jni.h>
#include quot;HelloWorld.hquot;
#include <stdio.h>
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *env, jobject obj)
{
printf(quot;Hello world!nquot;);
return;
}
- Total 17 pages - 1

41. HelloWorldImp.c
#include <jni.h>
#include quot;HelloWorld.hquot;
#include <stdio.h>
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *env, jobject obj)
{
printf(quot;Hello world!nquot;);
return;
}
- Total 17 pages - 1

42. HelloWorldImp.c
#include <jni.h>
#include quot;HelloWorld.hquot;
#include <stdio.h>
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *env, jobject obj)
{
printf(quot;Hello world!nquot;);
return;
}
- Total 17 pages - 1

43. Create a Shared Library
class HelloWorld {
...
System.loadLibrary(quot;helloquot;);
...
}
Compile the native code into a shared library:
(example for MS Windows Visual C++ 4.0)
cl -Ic:javainclude -Ic:javaincludewin32
-LD HelloWorldImp.c -Fehello.dll
- Total 17 pages - 1

44. Run the Program
Command:
java HelloWorld
Result:
Hello World!
Possible exceptions:
java.lang.UnsatisfiedLinkError: no hello in
shared library path at
java.lang.Runtime.loadLibrary(Runtime.java)
at java.lang.System.loadLibrary(System.java)
at java.lang.Thread.init(Thread.java)
- Total 17 pages - 1

45. Summary
Connect Java with native languages
Code reuse
Powerful
Compromise of Java safety features,

cross-platform and dynamic ability
JNI call is slow and costful

Not work well for applets

- Total 17 pages - 1

46. References
 Glenn L. Vanderburg. et al., Tricks of the Java
Programming Gurus, 1996, http://docs.rinet.ru:8080/
JaTricks/
 Beth Stearns, Trail: Java Native Interface, Sun
Microsystems, Inc., 2003, http://java.sun.com/docs/
books/tutorial/native1.1/
 Roedy Green, JNI, The Java Native Interface, Canadian
Mind Products, 2002, http://mindprod.com/jni.html
 Kong Wenyu, A Brief Introduction to Java Native
Interface, http://www.geocities.com/kongwenyu/jni.html
- Total 17 pages - 1

47. Questions?
- Total 17 pages - 1

48. Questions?
- Total 17 pages - 1