Reorganizig code on sieve of Eratosthenes

Question

I need help on reorgaizing my code.
import java.io.*;
import java.text.DecimalFormat;
public class sieve
     public static void main(String args[]) throws IOException
                    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
          System.out.print("Enter the primes upper bound  ===>>  ");
          int MAX = Integer.parseInt(input.readLine());
          double sqrt=0;
          MAX++;
          boolean primes[] = new boolean[MAX];
          computePrimes(primes);
          displayPrimes(primes);
          System.out.println();
     public static void computePrimes(boolean [] primes)
          System.out.println();
          System.out.println("Computing prime numbers\t");
          System.out.println();
          int MAX=primes.length;
          double sqrt=Math.sqrt(MAX);
          for(int i = 2; i < MAX; i++)
               primes[i] = true;
          for(int i = 2; i <= sqrt; i++)
               for(int j = i*2; j < MAX; j+=i)
                    primes[j] = false;
     public static void displayPrimes(boolean [] primes)
     DecimalFormat threeDigits= new DecimalFormat("000");
     final int MAX=primes.length;
     int r=MAX-1;
     System.out.println("\n Prime numbers between 1 and " + r + "\n");
          for(int i = 0; i < primes.length; i++)
               if(primes)
                    System.out.print(threeDigits.format(i) + "\t");
For the main method heading, it is supposed to go like:
public static void main(String args[]) throws IOException
                    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
          System.out.print("Enter the primes upper bound  ===>>  ");
          final int MAX = Integer.parseInt(input.readLine());
          boolean primes[] = new boolean[MAX];
          computePrimes(primes);
          displayPrimes(primes);
I'm not supposed to add anything to the main method heading, but if I don't my code doesn't work. Could somebody advise me on how I should reorganize my code, but still keep the general format? Thank you!

Answer 1

You don't need sqrt in main. It's never used.
And you don't need MAX++. I assume MAX is the highest number to test.
Lets say MAX is 5, and we create an array of 5 elements. Their indices are 0, 1, 2, 3, 4. Well, zero isn't even a candidate for being a prime. (Neither is 1, for that matter.) So we can put the results for 1 into slot 0, etc. up to results for 5 into slot 4.
And you don't need the System.out.println in main. If you want to print an extra line, do it in the display method.
Is that what you mean? If not, please clarify. "Doesn't work" carries zero information, or near enough as makes no difference.