Question

I am learning java with BlueJ, and recently I was given a .jar file called Imagen.jar. Apparently, what it does is return some pixel vectors depending on image file names given as parameters to it.

Anyway, I am supposed to make a program that will use a class called Imagen. Apparently, such class is within the mentioned .jar file.

Clearly, BlueJ won’t compile if I’m using such class since I have not imported it or anything. But, I don’t really know how to import such class in the first place.

I was given the following example code:

import java.io.PrintWriter;

public class Main {
   public static void main(String arg[ ]){
      if(arg.length > 1){
         Imagen imagen = new Imagen(arg[0]);
         int [][] m = imagen.getMatriz();
         PrintWriter salida = null;
         try {
             salida = new PrintWriter(arg[1]);  
         }
         catch(Exception e){
            System.err.println(e);   
         }
         for(int [] fila : m ){
            for(int valor : fila){
               System.out.print("\t"+valor);
               salida.print("\t"+valor);
            }   
            salida.println("");
            System.out.println("");
         }
         if(salida!=null){
            salida.close();
         }
      }
      else {
         System.out.println("Uso: java -classpath .;Imagen.jar Main nombreArchivo.gif");  
      }
   }
}

Which does not compile using BlueJ. However, as you can see, at the end it says that to use it, you have to type in the terminal:

java -classpath .;Imagen.jar Main myImageFile.gif

And I do it. But it keeps throwing me the same message.

So I am stuck right now:

• Why is the terminal line I was told to use not working?
• How can I import the class that is contained within a .jar file?

Answer 1

You need to do the following once.

Select the menu option Tools -> Preferences.
In the resulting dialog, click on the Libraries tab.

Click the Add button.
Navigate to the folder containing jar file. Select jar file.
Restart BlueJ.

Answer extracted from this place