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2025-01-07 22:00:12 +05:30
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Codes/Group A/Assignment-A3/A3.c
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#include <jni.h>
#include <stdio.h>
#include "A3.h"
// NOTE: The contents of this file can be referenced from A3.h which is the generated header file
// Refer explanation for more info: https://git.kska.io/sppu-te-comp-content/SystemsProgrammingAndOperatingSystem/src/branch/main/Codes/Group%20A/Assignment-A3/EXPLANATION.md
JNIEXPORT jint JNICALL Java_A3_add(JNIEnv *env, jobject obj, jint a, jint b) { // Function for addition
jint result = a + b;
printf("\n%d + %d = %d\n", a, b, result);
return result; // Return the result
}
JNIEXPORT jint JNICALL Java_A3_sub(JNIEnv *env, jobject obj, jint a, jint b) { // Function for subtraction
jint result = a - b;
printf("\n%d - %d = %d\n", a, b, result);
return result; // Return the result
}
JNIEXPORT jint JNICALL Java_A3_mul(JNIEnv *env, jobject obj, jint a, jint b) { // Function for multiplication
jint result = a * b;
printf("\n%d * %d = %d\n", a, b, result);
return result; // Return the result
}
JNIEXPORT jint JNICALL Java_A3_div(JNIEnv *env, jobject obj, jint a, jint b) { // Function for division
if (b == 0) {
printf("Error: Division by zero.\n");
return 0; // Return 0 or handle error appropriately
}
jint result = a / b;
printf("\n%d / %d = %d\n", a, b, result);
return result; // Return the result
}
Codes/Group A/Assignment-A3/A3.h
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// WARNING!!!
// THIS FILE IS INCLUDED ONLY FOR REFERENCE
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class A3 */
#ifndef _Included_A3
#define _Included_A3
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: A3
* Method: add
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_A3_add
(JNIEnv *, jobject, jint, jint);
/*
* Class: A3
* Method: sub
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_A3_sub
(JNIEnv *, jobject, jint, jint);
/*
* Class: A3
* Method: mul
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_A3_mul
(JNIEnv *, jobject, jint, jint);
/*
* Class: A3
* Method: div
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_A3_div
(JNIEnv *, jobject, jint, jint);
#ifdef __cplusplus
}
#endif
#endif
Codes/Group A/Assignment-A3/A3.java
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// Importing basic stuff
import java.io.*; // Used for I/O operations
import java.util.*; // Contains basic utilities
class A3 {
// Class name has to be same as file name for Java
static {
// Used for loading the .so (on Linux) or .dll (on Windows) file when running
// This is the main so called "dynamic library"
System.loadLibrary("A3");
}
// Function declaration
// private indicates the function is private, duh!
// Use of native indicates the function body will be written in a language other than Java, such as C/C++
private native int add(int a, int b); // For addition
private native int sub(int a, int b); // For subtraction
private native int mul(int a, int b); // For multiplication
private native int div(int a, int b); // For division
public static void main(String[] args) { // the main function
Scanner sc = new Scanner(System.in); // For taking input
int a, b;// Declaring variables for calculation
int choice = 0; // Declaring variable for switch-case
// Take input for a and b values
System.out.print("\nValue of a:\t");
a = sc.nextInt();
System.out.print("\nValue of b:\t");
b = sc.nextInt();
// Main menu
while (true) {
System.out.println("----- MAIN MENU -----");
System.out.println("1 -> Addition");
System.out.println("2 -> Subtraction");
System.out.println("3 -> Multiplication");
System.out.println("4 -> Division");
System.out.println("5 -> Exit");
System.out.println("Choose an option:\t");
choice = sc.nextInt();
switch (choice) {
case 1:
System.out.println("Result: " + new A3().add(a, b));
break;
case 2:
System.out.println("Result: " + new A3().sub(a, b));
break;
case 3:
System.out.println("Result: " + new A3().mul(a, b));
break;
case 4:
System.out.println("Result: " + new A3().div(a, b));
break;
case 5:
System.out.println("## END OF CODE");
System.exit(0);
default:
System.out.println("Please choose a valid option.");
break;
}
}
}
}
Codes/Group A/Assignment-A3/EXPLANATION.md
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# Explanation
This file contains explanation for dynamic linking library program (Assignment-A3)
---
Please note the files referred in this guide:
- [A3.java](https://git.kska.io/sppu-te-comp-content/SystemsProgrammingAndOperatingSystem/src/branch/main/Codes/Group%20A/Assignment-A3/A3.java)
- [A3.c](https://git.kska.io/sppu-te-comp-content/SystemsProgrammingAndOperatingSystem/src/branch/main/Codes/Group%20A/Assignment-A3/A3.c)
- [A3.h](https://git.kska.io/sppu-te-comp-content/SystemsProgrammingAndOperatingSystem/src/branch/main/Codes/Group%20A/Assignment-A3/A3.h)
---
- We're using Java for writing the main program.
- To demonstrate Dynamic Linking Library (DLL) in Java, we'll be declaring functions in Java and implementing them in C (can be C/C++).
- First, we create a Java program `A3.java`,
- This is the main Java file containing function definition and the main function.
- Functions (add, sub, mul, div) in `A3` class in this file are native functions, meaning their body is written in C/C++ in a different file.
- After creating this file, you need to compile it. To do so, run `javac A3.java` (assuming you're already in the directory that contains this file).
- Now, we will generate the header file. For this, run `javac -h . A3.java`.
- There will be a new file called `A3.h` in your current working directory,
- This is the header file.
- It contains signatures for native functions we created in the Java file.
- Thus, there's **no need to memorized boilerplate in `A3.c`** since the functions defined in that file can be found in the header file. I have included the [A3.h](https://git.kska.io/sppu-te-comp-content/SystemsProgrammingAndOperatingSystem/src/branch/main/Codes/Group%20A/Assignment-A3/A3.h) file in this folder for reference. Note that it is automatically generated.
- Create a new `A3.c` file which is the C program file containing function definitions (for add, sub, mul, div)
- Define all the functions (add, sub, mul, div)
- Then, we have to compile the C program file, i.e. `A3.c`. For this, run `gcc -shared -o libA3.so -fPIC -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" A3.c`,
- `gcc` -> GNU compiler for C program
- `-shared` -> tells the compiler to create a shared file (.so) instead of a regular executable file
- `-o libA3.so` -> tells the compiler to save the output to `libA3.so` file
- `fPIC` -> stands for Position-Independent Code. Needed for creating shared libraries.
- `-I"$JAVA_HOME/include"` and `-I"$JAVA_HOME/include/linux"` -> `-I` flag used for specifiying directories to include. Values in double quotes are directories
- `A3.c` -> name of the C program file to compile
- Lastly, run the program using `java -Djava.library.path=. A3`
- `java` -> Loads Java Virtual Machine (JVM)
- `-Djava.library.path=.` -> `-D` is used to set a system property. In this case, we’re setting the `java.library.path` (for .so or .dll files) property.
- `A3` -> name of the Java class containing the main method
---
Codes/Group A/Assignment-A3/README.md
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## Steps to run this code
These are the steps to run code for Assignment-A3.
---
### Refer [EXPLANATION](https://git.kska.io/sppu-te-comp-content/SystemsProgrammingAndOperatingSystem/src/branch/main/Codes/Group%20A/Assignment-A3/EXPLANATION.md) to understand how everything works.
> [!IMPORTANT]
> Tested on Linux and Windows.
### Prerequisites
1. open-jdk (version 11 or higher)
2. gcc
3. Set open-jdk and gcc as environment variables using bin folder in path (For Windows Users only)
4. Common sense
### Steps For Linux
1. Compile `A3.java`:
```shell
javac A3.java
```
2. Generate header file:
```shell
javac -h . A3.java
```
3. Compile C code:
```shell
gcc -shared -o libA3.so -fPIC -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" A3.c
```
> [!NOTE]
> If you get an error saying _"fatal error: jni.h: No such file or directory"_, this might be because you haven't set `$JAVA_HOME` environment variable. Usually JVM stuff is in `/usr/lib/jvm/java-<version>-openjdk-amd64`. To set `JAVA_HOME` environment variable, run: `export $JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64` (for version 17, adjust for your version accordingly.)
4. Run program:
```shell
java -Djava.library.path=. A3
```
### Steps For Windows
1. Compile `A3.java`:
```shell
javac A3.java
```
2. Generate header file:
```shell
javac -h . A3.java
```
3. Set `JAVA_HOME` to the path of your jdk file location:
> Note that this is my file location for jdk. It may differ for you.
```shell
set JAVA_HOME=C:\Program Files\openjdk-23.0.1_windows-x64_bin\jdk-23.0.1
```
4. Compile C code:
```shell
gcc -shared -o A3.dll -fPIC -I"%JAVA_HOME%\include" -I"%JAVA_HOME%\include\win32" A3.c
```
5. Run program:
```shell
java -Djava.library.path=. A3
```