Java Code problem

BrokenArrows

Im getting this error and cannot see why.

Can anyone help me. Thanks.

Robot.java:30: non-static variable this cannot be referenced from a static context

import josx.platform.rcx.*;
import java.lang.*;
import josx.robotics .*;




public class Robot

{
  int i=100;
  int id = 0;
  int light = 0;
  int total = 0;
  int cnt = 0;
  int average = 0;


  
  public static void main (String[] args)
  throws Exception
  {  
   	 	
	 	
  	 Motor.A.setPower(3);
  	 Motor.C.setPower(3);
  	 Motor.A.forward();
  	 Motor.C.forward();

	 LightDetect LD = new LightDetect();
	 LD.start(); 
  }

        public static void Stop()
	throws Exception
	{
		Motor.A.stop();
		Motor.C.stop();
	}

	public static void Turn(int degrees)
	throws Exception
	{
		Stop();
		
		Sensor.S3.setTypeAndMode(4,0xE0);
   		Sensor.S3.activate();
   		int tmp = Sensor.S3.readSensorValue(2,1);
   
   		Motor.A.setPower(5);
   		Motor.C.setPower(5);

   		Motor.C.forward();
   		Motor.A.backward();

   		while (Sensor.S3.readSensorValue(2,1)-tmp<degrees/5.4) {
    			LCD.showNumber(Sensor.S3.readSensorValue(2,1));
   		}

   		Stop();
   		Stop();
		Motor.A.setPower(3);
   		Motor.C.setPower(3);
		
		
	}

	public class LightDetect extends Thread
	{
	    public void run(){		
	    	Sensor.S1.setTypeAndMode(SensorConstants.SENSOR_TYPE_LIGHT,
       				SensorConstants.SENSOR_MODE_PCT); 
   		Sensor.S1.activate();
   		id = Sensor.S1.getId();
	
		while (i>0) {
    			total = 0;
    			for(cnt=0;cnt<10;cnt++){
    				light = Sensor.S1.readSensorValue(id,0);
        			total = total + light;
    			}
        		average = total / 10;
        		LCD.showNumber(average);
     
       			if(average > 760 && average < 790){
          			Stop();
	   			Turn(180);   
			}
        
        		if(average > 660 && average  < 690){
	   			Stop();
           			Motor.A.forward();
   	   			Motor.C.forward();
			}	   
		}// End while
     
            }
    	} //end LightDetect();
			

}

PhantomBeaker

BrokenArrows wrote:

Robot.java:30: non-static variable this cannot be referenced from a static context

[code]
public static void main (String[] args)
throws Exception
{


Motor.A.setPower(3);
Motor.C.setPower(3);
Motor.A.forward();
Motor.C.forward();

LightDetect LD = new LightDetect();
LD.start();
}

Ok, perversely line 30 is the LightDetect one - which doesn't appear to be a problem. At least the 30th line from when I paste it into a text editor.

Anyway, where do you declare Motor.A and Motor.C in your class? They're not passed in anywhere, and don't seem to be declared in the class anywhere. That looks to be your main problem - so you need to declare your variables/objects somewhere and then start passing them to the other methods that need to see them (like your stop() method).

Hope that helps a bit,
Aoife

zoro

It's actually pretty simple to fix

I'm assuming that LightDetect extends Thread here by the way (it appears so anyway)
When the compiler says line 30, you should check lines 29, 30 and 31 - it's not always on the button for some reason

Anyway - add this:

LightDetect LD = new LightDetect();
new Thread(LD).start();

You can't explicitly call LightDetect.start() as it's a non-static method (you're inside a static method when you call it;

That should work fine.
If it doesnt, try:

public static void main (String[] args) throws Exception
{
 new MyRobotClass();
}

public MyRobotClass() throws Exception
{
  Motor.A.setPower(3);
  Motor.C.setPower(3);
  Motor.A.forward();
  Motor.C.forward();

  LightDetect LD = new LightDetect();
  LD.start();
}

madramor

The first way zoro said will not work because its the same

The second way will because it takes any call to a non-static
variable or method out of the static method main.

The simpliest way is to take the class LightDetect out of the
class robot and put it in its own class file.

BrokenArrows

thanks for the help. This will help me in the future anyway.

I ended up rewriting the code as there are a few things i did not take into account.

zoro

madramor wrote:

The first way zoro said will not work because its the same

*slaps forehead* doh!

Oopies

madramor

BrokenArrows wrote:

I ended up rewriting the code as there are a few things i did not take into account.

look at the code zoro posted, none of your classes have constructors

also

public static void main (String[] args) throws Exception
{
 new MyRobotClass();
}

main shouldn't throw exceptions it should be

public static void main (String[] args){
   try{
      new MyRobotClass();
   }
   catch(Exception e){
      // handle
   }
}