Sophomore Java Homework-P4.18 v3

/**
 * Name: List of prime numbers-store prime factors in array
 * @author LinChuWen
 * Date: 2014.10.16
 *
 * NCHU EE,course number:2335
 * course name: Object Oriented Language
 * Textbook: Big Java:Late Objects-Cay S. Horstmann
 * Problem: P4.18
 * Description: Enter an integer "n", then prints out all prime numbers up to that integer.
 */
import java.util.*;
public class HW3_P4_18_v3 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int n;

        System.out.print("Please enter an integer: ");
        while(input.hasNext()){
            n=input.nextInt();
            long startTime = System.currentTimeMillis();

            if(n>4)
                list_prime(n);
            else
                n_less_than_5(n);

            long endTime = System.currentTimeMillis();
            long totTime = endTime - startTime;
            System.out.println("Using Time:" + totTime + " ms");
            System.out.print("Please enter an integer: ");
        } //while end

        input.close();
    } //main end

    static void list_prime( int number ){
        System.out.printf("2\n3\n");
        int d_sqrt;                 //square root of dividend
        int dividend;               //dividends that counting up to user's input "n"
        int[] prime_factors = new int[1000000]; //array that store prime factors
        prime_factors[0]=2;prime_factors[1]=3;  //set first two prime factors to "2" and "3"
        int index=1;                //index of array "prime_factors3u6j5/4[]"
        int cnt;                //counter use in small for loop
        boolean prime;              //flag use in small for loop

        for(dividend=5;dividend<=number;dividend+=2){
            prime=true;
            d_sqrt=(int)Math.sqrt(dividend);
            for(cnt=1;cnt<=index;cnt++){
                if(prime_factors[cnt]>d_sqrt)
                    break;

                if(dividend%prime_factors[cnt]==0){
                    prime=false;
                    break;
                } //if end
            } //small for end

            if(prime){
                System.out.println(dividend);
                index++;
                prime_factors[index]=dividend;
            } //if(prime) end
        } //big for end

        return;
    } //list_prime() end

    static void n_less_than_5( int n ){
        if(n<0)
            System.out.println("Please enter a positive integer!");
        else if(n==0 || n==1)
            System.out.println("No prime numbers up to " + n);
        else if(n==2)
            System.out.println(2);
        else if(n==3 || n==4)
            System.out.printf("2\n3\n");
        return;
    } //n_less_than_5() end

} //class end