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Lab 1 Java Panama Hello World

The objective of this lab is use jextract to generate Panama code and successfully execute an existing Java Hello World example. The following are the exercises for Lab 1:

  • Exercise 1 - Generate classes for stdio.h
  • Exercise 2 - Generate source code for stdio.h
  • Exercise 3 - Execute the existing HelloWorld.java file
  • Exercise 4 - (Optionally) Setup your IDE

C Hello World

The following is C Source code of a Hello World application that is shown as a reference. Your task is to generate binding code so that the Java application can invoke C functions natively similar to the C version of Hello World.

#include <stdio.h>                
int main() {                      
   printf(“Hello, World! \n”);    
   return 0;                      
}

Before you begin change directory to lab1 and run the following scripts to clean up: Linux and MacOS

bash clean.sh

Windows

clean_windows.cmd

The following are the parameters when using the jextract tool.

  • classes - Destination of class files
  • src - Destination of source files
  • org.unix - Package namespace
  • $C_INCLUDE_PATH - C include directory path
  • $C_INCLUDE_PATH/stdio.h - The location of the header file

If you are unsure what the jextract options are type:

jextract -h

If you get an error your JAVA_HOME is probably not setup properly. Refer to Setup Develpment Environment Instructions

Exercise 1: Generate classes using jextract against stdio.h

After classes are generated directories should look like the following:

 |-- classes
 |    |-- org
 |        | unix

Exercise 2: Generate source code using jextract for stdio.h

After source files are generated directories should look like the following:

 |-- src
 |   |-- org
 |       |-- unix

Exercise 3: Execute the Java file HelloWorld.java

java -cp classes --enable-native-access=ALL-UNNAMED --add-modules jdk.incubator.foreign src/HelloWorld.java

  • classes - Classpath
  • ALL-UNNAMED - enable native access
  • jdk.incubator.foreign - Module to add
  • src/HelloWorld.java or src\HelloWorld.java - Java application

After executing the Java application the following should output should be:

Hello World! Panama style
(Java) Hello World! Panama style

Exercise 4: (Optional) Setup your IDE

Set Java compiler to point to use Panama’s JDK Compiler JVM options (--add-modules jdk.incubator.foreign)

Excercise 4: (Optional) Compile and Run helloworld.c

Do the following:

gcc helloworld.c

outputs:

a.out

#Windows
a.out.exe

To run

./a.out