# How to create an executable java application?

• Java

## Main Question or Discussion Point

Hi, I've recently written a small program to calculate multiplicative group tables for Z mod n. I wrote it in java, as that's the only programming language I currently know.

Code:
import java.util.*;

public class ZnX
{

public static int gcd(int a, int b)
{

if (b==0)
return a;
else
return gcd(b, a % b);
}

public static void main(String[] args)
{
final int TWO_DIGITS = 10;

int n = 0;
int[] primes = new int[0];

System.out.println("Multiplication table for Z modulo n");

Scanner scan = new Scanner(System.in);

// Calculating Relatively Prime Integers
while(scan.hasNextInt())
{
if(scan.hasNextInt())
{
n = scan.nextInt();
primes = new int[n];
//           System.out.print("The set of relatively prime integers to " +  n + " is: {");
}
else
{
System.out.println("Input is not an integer, terminating program");
System.exit(0);
}

int j = 0;
for(int i = 0; i <= n; i++)
{
if(gcd(i,n) == 1)
{
primes[j] = i;
//                System.out.print(i + ", ");
j++;
}
}

//        System.out.println("}");
//        System.out.println("Number of elements: " + j);

System.out.println("The multiplication table for Z modulo " + n + " is:");

int[][] multTable = new int[j][j];
for(int row = 0; row < j; row++)
{
for(int col = 0; col < j; col++)
{
multTable[row][col] = (primes[row] * primes[col]) % n;
System.out.print(multTable[row][col]);

if((multTable[row][col]) < TWO_DIGITS)
System.out.print("  ");
else
System.out.print(" ");
}
System.out.print("\n");

} // End for loop

}  // End while loop

System.out.println("End of valid integers, terminating program");

} // End main
} // End class
This code compiles and runs correctly from the commandline. Now, because I'm writing this for my computer illiterate math teacher, I'd like to create an executable file (.jar?) which she can simply double click to run

Is there any way to do this without using GUI/applets?

Thanks!

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Eus
Hi Ho!

Sure, your teacher can run your Java program just by double-clicking the JAR file.

The complete information is here:
http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html
http://java.sun.com/j2se/1.4.2/docs/guide/jar/jar.html [Broken]

Basically, just create a jar with the following structure:
+-- META-INF/ -- MANIFEST.MF
|
+-- ZnX.class
with the following command:
Code:
jar cvfm ZnX.jar MANIFEST.MF ZnX.class
Notice that you have to create a text file named MANIFEST.MF prior to running the command above. The file should contain the following lines:
Code:
Manifest-Version: 1.2
Main-Class: ZnX
Created-By: 1.4 (Sun Microsystems Inc.)
Good luck!

Best regards,
Eus

Last edited by a moderator:
Thanks for the tips, Gus!

Could you try it out using my code? When I double click the jar file, it doesn't seem to do anything. No errors, but no output either

I was hoping that the program would run in the terminal like it normally does. Is this because I don't use any GUI?

Eus
Thanks for the tips, Gus!

Could you try it out using my code? When I double click the jar file, it doesn't seem to do anything. No errors, but no output either

I was hoping that the program would run in the terminal like it normally does. Is this because I don't use any GUI?

I had tried it and I could run the JAR file nicely in the command line with the following command:

Code:
java -jar ZnX.jar
If you try to run the JAR file by double-clicking on the file and you use Windows, the icon of the JVM should appear in the tray icon.
Otherwise, there might be something wrong with the setting of your JVM under Windows.

Good luck!

Best regards,
Eus