Prime Generator v2- runs in CodeChef

1. This one passes through CodeChef's judge in 8.36 seconds, still 2.36 seconds slower than it should.
   
   

   import java.util.*;import java.io.*;
   public class Main {
   /** * @param args the command line arguments */ static LinkedHashSet<Integer> primes = new LinkedHashSet<Integer>();
   
   public static void main(String[] args) throws Exception{ //for(int i = 2; i<100000; i++) // if(isPrime(i)) // primes.add(i);
   
   BufferedReader k = new BufferedReader(new InputStreamReader(System.in));
   int m = Integer.parseInt(k.readLine());
   for(int i =1; i<=m; i++){ if(i!=1) System.out.println("\n");
   StringTokenizer st = new StringTokenizer(k.readLine());
   int a = Integer.parseInt(st.nextToken());
   int b = Integer.parseInt(st.nextToken());
   boolean first = true;
   for(int j = a; j<=b; j++ ){ if(isPrime(j)){ primes.add(j);
   if(first){ first=false;
   System.out.print(j);
   } else System.out.print("\n"+j);
   } } }
   } static boolean isPrime(int n){ if(n<2) return false;
   
   
   double d = Math.sqrt(n);
   
   for(Integer p: primes){ if(p>d) break;
   if(n%p==0)
   return false;
   } return true;
   }
   }

SPOJ's Prime Generator - Time Limit Exceeded

Well, I must rethink this...


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;


/**
 *
 * @author antonio
 */
public class Main {


    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws IOException{
        // TODO code application logic here


        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));


        int cases = Integer.parseInt(br.readLine());


       BigInteger lower;
       BigInteger upper;
       BigInteger intermediate;


        for (int i=0; i<cases; i++){


            String [] splitted = br.readLine().split(" ");
            lower = new BigInteger(splitted[0]);


            if (lower.isProbablePrime(100)){
                System.out.println(splitted[0]);
            }


            upper = new BigInteger(splitted[1]);
            intermediate = lower.nextProbablePrime();




            while(intermediate.compareTo(upper)<=0){
                System.out.println(intermediate);
                intermediate = intermediate.nextProbablePrime();


            }


           System.out.println(" ");
        }


    }


}