I Messed Up With My Thread Code

[JiaPei Jen]

I am trying to use Thread to generate some random numbers and I got some compilation errors:

.\CustomizedRandomNumGenerator.java:6: cannot resolve symbol
symbol : variable start
location: class CustomizedRandomNumGeneratorService
service = new CustomizedRandomNumGeneratorService().start;
^
.\CustomizedRandomNumGenerator.java:18: cannot resolve symbol
symbol : variable ranNum
location: class CustomizedRandomNumGenerator
return ranNum;

I have a main program that is supposed to display 5 random numbers:

public class DisplayRandomNumbers
{
   public static void main( String[] args )
   {
      for ( int loopIndex = 0; loopIndex < 5; loopIndex++ )
      {
         RandomNumberGenerator ranGen = new CustomizedRandomNumGenerator();
         System.out.println( "Random number generated from running a thread: " + ranGen.getRandom() );
      }
   }
}

The RandomNumberGenerator is an interface with a getRandom(); method to be implemented:

public interface RandomNumberGenerator
{
   public double getRandom();
}

The CustomizedRandomNumGenerator implements the RandomNumberGenerator and starts a thread in the getRandom(); method. And it is the class where compilation errors occurred.

public class CustomizedRandomNumGenerator implements RandomNumberGenerator
{
   CustomizedRandomNumGeneratorService service;
   public double getRandom()
   {
      service = new CustomizedRandomNumGeneratorService().start;           
      for ( int i = 0; i < 10; i++ ) 
      {
         try
         {
            Thread.sleep(5);
         }
         catch( InterruptedException exception )
         {
            System.err.println( exception.toString() );
         }
      }
      return ranNum;          
   }
} 

The code in the CustomizedRandomNumGeneratorService looks like:

public class CustomizedRandomNumGeneratorService extends Thread 
{
   static double ranNum;
 
   public void run() 
   {
      while (true) 
      {
         if (ranNum == 1000)
         ranNum = 0;
         ranNum++;
      }
   }
}

[Ernest Friedman-Hill]

My goodness. You did say this had something to do with a job interview, didn't you? I suspect that you're going to have some real problems doing this job, if you get it. The answers to both of these are really very obvious.

Would you like to practice for your new job by thinking about these errors, and then posting your guesses in this thread -- or do you want us to just give you the answers? If you get a job as a programmer, you're going to have to get used to figuring this sort of thing out for yourself.

So what will it be?

[Jeff Bosch]

Hint #1: What's the difference in syntax when referring to an object's variable and invoking an object's method?

[Steven Bell]

I'm kinda with Ernest here. The code you have here shows many things, none of them good. My suggestion would be do delete the whole mess and spend a couple hours understanding how threads work.

P.S. the Thread.sleep(5) call in your code has no effect on your 'random number generater' thread.

[JiaPei Jen]

I have come up with a clean skeleton (without compilation error). But, the code does not generate random numbers as it is coded:

/**
 *
 *  CustomizedRandomNumGenerator implements the RandomNumberGenerator
 *  interface and starts running a thread.
 *
 */
public class CustomizedRandomNumGenerator implements RandomNumberGenerator
{
   double ranNum;      
   CustomizedRandomNumGeneratorService service;
 
   public double getRandom()
   {
      service = new CustomizedRandomNumGeneratorService();
      /**
       *
       *  The start() method causes the thread to begin execution.
       *
       *  @return     void
       *
       */
      service.start();
      return ranNum;
   }
} 

and

public class CustomizedRandomNumGeneratorService extends Thread 
{
   public CustomizedRandomNumGeneratorService()
   {  
      super();
   }
   /*  execute the thread  */
   public void run() 
   {
      try
      {
         /**
          *  put the currently executing thread to sleep.
          *
          *  @param    5 milliseconds with the long primitive type
          *  @return   void
          * 
          */
         Thread.sleep(5);
      }
      catch( InterruptedException exception )
      {
         System.err.println( exception.toString() );
      }
   }
}

[Henry Wong]

Hint: What is the variable that you are returning as a random number? And what is the variable you are using to generate the random number? ...

Henry