write a program to print all the prime numbers up to a given number ?

import java.io.*;

class primenumber
{
 public static void main(String a[]) throws Exception
 {
  System.out.println("Welcome to the primenumber project!");
  BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  System.out.println("Enter Upper Bound Number");
  int N = Integer.parseInt(br.readLine());
  int i=0,j=0;
  int flag=1;
  System.out.print("2\t3\t");
  for(i=4;i<N;i++){
      for(j=2;j<=Math.sqrt(i);j++){
          if(i%j==0){
              flag=0;
              break;
          }
      }
      if(flag==1){
          System.out.print(i+"\t");
      }
      flag=1;
  }
  System.out.println();
 }
 
}

http://www.programmr.com/Java/prime_number-5