Running a JAR file in Pi results in following error "can't find the main class"

Question

I want to make a GUI application in java which can control the gpio pins. I used pi4j lib for control the pins. I wrote a pin toggle code inside the button click event as shown below. while running JAR file in Pi it showing the error as "can't find the main class". I would like to know whether it is possible to write the gpio control code in click event...pls help..

package javatest;
import com.pi4j.io.gpio.GpioController;
import com.pi4j.io.gpio.GpioFactory;
import com.pi4j.io.gpio.GpioPinDigitalOutput;
import com.pi4j.io.gpio.PinState;
import com.pi4j.io.gpio.RaspiPin;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
/**
 *
 * @author R
 */
public class Javatest extends javax.swing.JFrame {
private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) { 
 // TODO add your handling code here:
 imageCross = new javax.swing.ImageIcon(cross);
 imageCircle = new javax.swing.ImageIcon(circle);
 if (a==0){
 jButton4.setIcon(imageCross);
 a=1;
 }
 else{
 jButton4.setIcon(imageCircle);
 a=0;
 }
 try {
 System.out.println("PC1<--Pi4J--> GPIO Control Example ... started.");
 // create gpio controller
 final GpioController gpio = GpioFactory.getInstance();
 Thread.sleep(5000);
 System.out.println("PC2<--Pi4J--> GPIO Control Example ... started.");
 // provision gpio pin #01 as an output pin and turn on
 final GpioPinDigitalOutput pin = gpio.provisionDigitalOutputPin(RaspiPin.GPIO_01, "MyLED", PinState.HIGH);
 System.out.println("--> GPIO state should be: ON");
 Thread.sleep(5000);
 // turn off gpio pin #01
 pin.low();
 System.out.println("--> GPIO state should be: OFF");
 Thread.sleep(5000);
 // toggle the current state of gpio pin #01 (should turn on)
 pin.toggle();
 System.out.println("--> GPIO state should be: ON");
 Thread.sleep(5000);
 // toggle the current state of gpio pin #01 (should turn off)
 pin.toggle();
 System.out.println("--> GPIO state should be: OFF");
 Thread.sleep(5000);
 // turn on gpio pin #01 for 1 second and then off
 System.out.println("--> GPIO state should be: ON for only 1 second");
 pin.pulse(1000, true); // set second argument to 'true' use a blocking call
 // stop all GPIO activity/threads by shutting down the GPIO controller
 // (this method will forcefully shutdown all GPIO monitoring threads and scheduled tasks)
 gpio.shutdown();
 } catch (InterruptedException ex) {
 Logger.getLogger(Javatest.class.getName()).log(Level.SEVERE, null, ex);
 }
public static void main(String args[]) {
 /* Set the Nimbus look and feel */
 //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
 /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
 * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
 */
 try {
 for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
 if ("Nimbus".equals(info.getName())) {
 javax.swing.UIManager.setLookAndFeel(info.getClassName());
 break;
 }
 }
 } catch (ClassNotFoundException ex) {
 java.util.logging.Logger.getLogger(Javatest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
 } catch (InstantiationException ex) {
 java.util.logging.Logger.getLogger(Javatest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
 } catch (IllegalAccessException ex) {
 java.util.logging.Logger.getLogger(Javatest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
 } catch (javax.swing.UnsupportedLookAndFeelException ex) {
 java.util.logging.Logger.getLogger(Javatest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
 }
 //</editor-fold>
 //</editor-fold>
 /* Create and display the form */
 java.awt.EventQueue.invokeLater(new Runnable() {
 public void run() {
 new Javatest().setVisible(true);
 }
 });
 }
 // Variables declaration - do not modify 
 private javax.swing.JButton jButton2;
 private javax.swing.JButton jButton3;
 private javax.swing.JButton jButton4;
 private javax.swing.JButton jButton5;
 // End of variables declaration 
}

• rob: what command are you using to run it?

Answer 1

Use java -cp myjar.jar javatest.Javatest

first argument after '-cp' is the jar file, 
second is the classpath to class containing main(String[]) method

If you dont have a MANIFEST in your jar file, you need to specify which class contains the main(String[] args) method. If you want to avoid it in the future, and be able to run a jar via doubleclick (non console) read How to create a MANIFEST file

• user27849: it still showing the same error
• thekiwi5000: Make sure thet Javtest.java file is in /javatest sirectory in your jarfile. If ths doesn't work, just run the classfile instead of jar. Please post screenshot of your jarfile file hierarchy opened in archive viewer.

Answer 2

You didn't mention what parameters you were passing to Java but I suspect that you are not including PI4J on your classpath.

You need to include the following:

.:/opt/pi4j/lib/'*'

for example

java -cp .:/opt/pi4j/lib/'*' javatest/Javatest