JAVA - Creating, running, and setting the characteristics of a thread

Calculator.java

import java.io.FileWriter;

public class Calculator implements Runnable
{
   @Override
   public void run()
   {
      long current = 1L;
      long max = 20000L;
      long numPrimes = 0L;
      
      System.out.printf( "Thread '%s': START\n",
                        Thread.currentThread().getName() );
      while ( current <= max )
      {
            if ( isPrime( current ) )
            {
                  numPrimes++;
            }
            current++;
      }
      System.out.printf( "Thread '%s': END. Number of Primes: %d\n", 
                         Thread.currentThread().getName(), numPrimes );
   }
   
   private boolean isPrime( long number )
   {
      if ( number <= 2 )
      {
            return true;
      }
      for ( long i = 2; i < number; i++ )
      {
            if ( ( number % i ) == 0 )
            {
               return false;
            }
      }
      return true;
   }
}

Main.java

// Creating, running, and setting the characteristics of a thread

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.lang.Thread.State;

public class Main
{
   public static void main( String[] args )
   {
      System.out.printf( "Minimum Priority: %s\n", 
                         Thread.MIN_PRIORITY );
      System.out.printf( "Normal Priority: %s\n", 
                         Thread.NORM_PRIORITY );
      System.out.printf( "Maximum Priority: %s\n", 
                         Thread.MAX_PRIORITY );
      
      Thread threads[];
      Thread.State status[];
      threads = new Thread[10];
      status = new Thread.State[10];
      
      for ( int i = 0; i < 10; i++ )
      {
         threads[ i ] = new Thread( new Calculator() );
         
         if ( ( i % 2 ) == 0 )
         {
            threads[ i ].setPriority(Thread.MAX_PRIORITY );
         } else {
            threads[ i ].setPriority(Thread.MIN_PRIORITY);
         }
            threads[ i ].setName( "My Thread " + i );
      }
      
      try ( FileWriter file = new FileWriter(".\\data\\log.txt");
      PrintWriter pw = new PrintWriter( file ); )
      {
         for ( int i = 0; i < 10; i++ )
         {
            pw.println( "Main : Status of Thread " + i + " : " + threads[ i ].getState() );
            status[ i ] = threads[ i ].getState();
         }
         
         for ( int i = 0; i < 10; i++ )
         {
            threads[ i ].start();
         }
         
         boolean finish = false;
         
         while ( !finish ) {
            for ( int i = 0; i < 10; i ++ )
            {
               if ( threads[ i ].getState() != status[ i ] )
               {
                  writeThreadInfo( pw, threads[ i ], status[ i ] );
                  status[ i ] = threads[ i ].getState();
               }
            }
            
            finish = true;
            for ( int i = 0; i < 10; i++ )
            {
               finish = finish && ( threads[ i ].getState() == State.TERMINATED );
            }
         }
      } catch ( IOException e )
      {
         e.printStackTrace();
      }
   }
   
   private static void writeThreadInfo( PrintWriter pw, Thread thread, State state )
   {
      pw.printf( "Main : Id %d - %s\n",  thread.getId(), thread.getName() );
      pw.printf( "Main : Priority: %d\n", thread.getPriority() );
      pw.printf( "Main : Old State: %s\n", state );
      pw.printf( "Main : New State: %s\n", thread.getState() );
      pw.printf( "Main : *************************************\n" );
   }
}