rotate() doesn't work (!)

[hyderabat]

Hi

I am really frustrated by now. I spent hours searching for an error, but I just can't find it.

I have separated the problem code from the rest and made an own program with it:

Code: Select all

     public static RemoteMotor [] mR;
   public static NXTRegulatedMotor [] m = {Motor.A,Motor.B,Motor.C};
   
   /**
    * @param args
    */
   public static void main(String[] args) {
      // TODO Auto-generated method stub
      
      try{
         RemoteNXT remo = new RemoteNXT("REMO",Bluetooth.getConnector());
         mR[0] =  remo.A; mR[1] = remo.B; mR[2] = remo.C;
   
      } catch (Exception e) {LCD.drawString("Damn",0,2);}
      
      workThing();
   }
   
   public static void workThing() {
      try {
      LCD.drawString("Starting",0,0);
      Button.waitForPress();
      mR[0].rotate(180,true);
      mR[2].rotate(180);
      Button.waitForPress(10000);
      
      do {
         mR[1].rotate(90,true);
         for (int i = 0;i<3;i++) m[i].rotate(360,true);
         m[2].waitComplete();
         //Delay.msDelay(270/50 * 1000); -> waitComplete() seems to work
         mR[1].rotate(-90);
         
      } while (Button.RIGHT.isPressed());
      } catch (Exception e) {LCD.drawString("Fucked up",0,4);}
      
      Button.waitForPress();

After "Starting", the system collapses and a NullPointerException (Exception 16) is thrown (before I did the try-catch myself). It is because of the rotate()-commands just following the "Starting". And if I comment them out, the same happens with the last rotate() in the loop.

Any clue why this happens with rotate? I am using rotate hundreds of times before in the same program, and it works perfectly. Only here and at another place does it collapse:

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while (true) {
      for (int i = 2;i>=0;i= i-1) {m[i].setSpeed(velocity); m[i].rotate(180);}
      for (int i = 2;i>=0;i= i-1) {mR[i].setSpeed(velocity); mR[i].rotate(180);}
      ErrorEscape();
      for (int i = 0;i<3;i++) {m[i].rotate(180,true); mR[i].rotate(180,true);}   
      ErrorEscape(); //have to get an error response as fast as possible, therefore twice in here
      }

Here, it is even stranger: the error is thrown with mR[1], after m[1-3] and mR[2] already worked perfectly!

[gloomyandy]

Almost certainly a problem with the RemoteMotor class which in 0.9.0 does not correctly handle the case of not having a listener call back. See the following threads for details...
viewtopic.php?f=7&t=2837&p=13881&hilit=+NullPointerException#p13881
viewtopic.php?f=7&t=2837&p=13854&hilit=remotemotor+null#p13854
viewtopic.php?f=7&t=2867&p=14097&hilit=motor+listener#p14097

Andy

[hyderabat]

I tried the following thing, just like Dominik said:

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import lejos.nxt.*;
import lejos.nxt.remote.*;
import lejos.nxt.comm.Bluetooth;
import lejos.nxt.remote.RemoteNXT;
import lejos.robotics.RegulatedMotor;
import lejos.robotics.RegulatedMotorListener;

public class TestIt {
   
   public static RemoteMotor [] mR;
   public static NXTRegulatedMotor [] m = {Motor.A,Motor.B,Motor.C};
   
   /**
    * @param args
    */
   public static void main(String[] args) {
      // TODO Auto-generated method stub
      
      try {
      RegulatedMotorListener [] Listener = new RegulatedMotorListener[6];
      for (int i = 0;i<3;i++) {m[i].addListener(Listener[i]);}
      for (int i = 3;i<6;i++) {mR[i-3].addListener(Listener[i]);}
      } catch (Exception e) {LCD.drawString("ListenerException",0,0);}
...
      

Threw a NullPointerException Do you need the upDownInitialized = true?! don't think so... and I don't have a clue what he is doing with this implement stuff^^

[gloomyandy]

You need to create a class that implements that motor listener interface (as shown in the first thread) and then create a single instance of that class, you then set this instance to be the listener for all three remote motors...

Andy

[hyderabat]

So, first, I have to use the class, looking like that:

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package TestingArea;

import lejos.robotics.RegulatedMotorListener;
import lejos.robotics.RegulatedMotor;

public class MotorListener implements RegulatedMotorListener{

   @Override
      public void rotationStarted(RegulatedMotor arg0, int arg1, boolean arg2,
            long arg3) {
         // TODO Auto-generated method stub
        
      }

      @Override
      public void rotationStopped(RegulatedMotor arg0, int arg1, boolean arg2,
            long arg3) {
    // TODO Auto-generated method stub
        
     }
}

I didn't change anything, as I suppose this is correct (only two methods in RegulatedMotorListener). Do I have to ajust anything here?

Then, I initialize the motors in the main class/where the rest happens:

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try {
      RegulatedMotorListener Listener = new MotorListener();
      for (int i = 0;i<3;i++) {mR[i-3].addListener(Listener);}
      } catch (Exception e) {LCD.drawString("ListenerException",0,0);}

Isn't working for me, as I can't even put the MotorListener() class on the brick I would really, really appreciate some detailed help here... Thanks!

[skoehler]

Code: Select all

try {
      RegulatedMotorListener Listener = new MotorListener();
      for (int i = 0;i<3;i++) {mR[i-3].addListener(Listener);}
      } catch (Exception e) {LCD.drawString("ListenerException",0,0);}

i-3 is clearly negative! Since Java arrays cannot have negative indexes, your code most certainly crashes with an ArrayIndexOutOfBoundsException and not with some sort of "ListenerException". If you want to know what Exception your actually catching, you might also write e.getClass().toString() to the Screen. It will not print the name, but it print the classes number.

[hyderabat]

You're right, the mistake came from previous code... But it doesn't change anything

Exception is class 16 -> still NullPointerException

BTW: In order to get the class MotorListener to the NXT, I just added an empty main()-loop below... can I do that?

[hyderabat]

Please, has anyone an idea? I would be really, really greatful. It is for a school project, and I can't get any further on my own as I am just getting to know LeJOS...

Here again the code in the main-file:

Code: Select all

try {
      RegulatedMotorListener Listener = new MotorListener();
      for (int i = 0;i<3;i++) {mR[i].addListener(Listener);}
      } catch (Exception e) {LCD.drawString(e.getClass().toString(),0,0);}

Then, I created an own file for the following class. I can't include it into the other file (as Eclipse told me).

Code: Select all

public class MotorListener implements RegulatedMotorListener{

   @Override
      public void rotationStarted(RegulatedMotor arg0, int arg1, boolean arg2,
            long arg3) {
         // TODO Auto-generated method stub
        
      }

      @Override
      public void rotationStopped(RegulatedMotor arg0, int arg1, boolean arg2,
            long arg3) {
    // TODO Auto-generated method stub
         }
      
      public static void main(String[] args) {
         // TODO Auto-generated method stub
         
      }
}

[gloomyandy]

Try the following code (you will have to change the name of the brick to match your second nxt)...

Code: Select all

import lejos.nxt.comm.Bluetooth;
import lejos.nxt.remote.RemoteNXT;
import lejos.robotics.RegulatedMotor;
import lejos.robotics.RegulatedMotorListener;

class Listener implements RegulatedMotorListener
{

    @Override
    public void rotationStarted(RegulatedMotor arg0, int arg1, boolean arg2,
            long arg3)
    {
        // TODO Auto-generated method stub       
    }

    @Override
    public void rotationStopped(RegulatedMotor arg0, int arg1, boolean arg2,
            long arg3)
    {
        // TODO Auto-generated method stub       
    }
   
}


public class RemoteTest
{

    /**
     * @param args
     */
    public static void main(String[] args) throws Exception
    {
        RegulatedMotorListener l = new Listener();
        RemoteNXT nxt = new RemoteNXT("nxt4", Bluetooth.getConnector());
        RegulatedMotor m = nxt.B;
        m.addListener(l);
        m.rotateTo(360);
    }
}


If you still get an exception. Post exactly what is displayed on the screen here (do not add any try/catch statements to the above code) and also include the verbose output from the linker (you may have to change your eclipse project settings to get leJOS to generate this output)...

Andy

[hyderabat]

After I changed a few things, I run the program on the NXT, and it worked perfectly. Thanks a ton for it, I could alter my own program following the general syntax of your program, and it works perfectly now Finally, my bloody school project is running... Thanks everyone for your help!!!