Having trouble printing an array of prime numbers that has been resized

Question

HI, im having trouble with my printPrimeNumbers() method printing the current state of an array, I can only get it to print the original state it was in. The array is inside of a primeNumbers object. I used checkAndResize to resize that array. my printPrimeNumbers method must be void without a parameter. How could i get my PrintPrimeNumbers method to print out a resized array without modifying the parameter? Any ideas.
Here is my PrimeNumbers class:
* Created by IntelliJ IDEA.
* User: Kevin
* Date: Mar 4, 2007
* Time: 1:53:56 AM
* To change this template use File | Settings | File Templates.
package primes;
public class PrimeNumbers {
    private boolean [] sieve;
    public PrimeNumbers(int  upper) {
        initializeSieve(upper);
    public int getNthPrime (int n){
    int prime = 0;
    double num;
    if (n >= sieve.length)
        checkAndResize(n + 1);
    for (int i = 0; i < sieve.length; i++){
        if(sieve)
prime++;
if (prime == n)
return i;
if (prime < n && i == sieve.length -1)
checkAndResize(2*sieve.length);
return -1;
public int getNumberPrimeNumbers(int n){
int primes = 0;
for (int i =0 ; i < sieve.length ; i ++){
if (n > sieve.length){
checkAndResize(n);
if(sieve[i])
primes++;
else if (sieve[i])
primes++;
return primes;
public int getSieveSize ()
return sieve.length;
public boolean isPrime (int n) {
if (n > sieve.length){
checkAndResize(n);
//initializeSieve(n);
return sieve[n];
// prints out the prime numbers inside sieve
public void printPrimeNumbers() {
int n = 0;
boolean first = true;
System.out.print("[");
for(int i = 0; i < sieve.length - 1; i++){
n++;
if(sieve[i] == true && n != sieve.length - 1) {
if(first) first = false;
else System.out.print(" ");
System.out.print(i);
System.out.println("]");
// checks length of sieve with N and then resizes sieve if nessecary.
private void checkAndResize (int n){
if ((n + 1) >= sieve.length){
initializeSieve(2*n);
private void setMultiples (int k) {
for (int i = 2*k; i < sieve.length; i += k)
sieve [i] = false;
private void initializeSieve (int upper){
if ( upper < 2)
sieve = new boolean [2];
else
sieve = new boolean [upper + 1];
sieve[0] = false;
sieve[1] = false;
for (int i =2 ; i< sieve.length; i ++ )
sieve[i] = true;
int bound = (int) Math.ceil(Math.sqrt(sieve.length));
for (int i = 2 ; i < bound ; i ++)
if (sieve[i])
setMultiples (i);
private String booleanToString (boolean value)
if (value)
return "T";
else
return "F";
public String toString (){
StringBuffer buf = new StringBuffer("[");
for (int i = 0; i < sieve.length -1 ; i ++)
buf.append(booleanToString (sieve[i]) + " " );
buf.append(booleanToString (sieve[sieve.length -1]) + "]");
return buf.toString();
here is the client code
        PrimeNumbers test = new PrimeNumbers(16);
        System.out.println(test);
        System.out.println("There are " + test.getNumberPrimeNumbers(16) +
                " prime nummbers in the sieve from 1 to 15. \n");
        System.out.println("There are " + test.getNumberPrimeNumbers(26) +
                "  prime numbers in the resized sieve from 1 to 25.");
        System.out.println("\nThe first 25 prime numbers are:");// makes sense why it doesnt work
        test.printPrimeNumbers();
        System.out.println("\nThe 13th prime number is: " + test.getNthPrime(13));
        System.out.println();
        System.out.println("The number 3001 is prime:  " + test.isPrime(3001));do you see how my methods resized it?
here is the output:
[F F T T F T F T F F F T F T F F F]
There are 6 prime nummbers in the sieve from 1 to 15.
There are 15 prime numbers in the resized sieve from 1 to 25.
The first 25 prime numbers are:
[2 3 5 7 11 13 17 19 23 29 31 37 41 43 47]// this is only the first 15 elements
The 13th prime number is: 41
The number 3001 is prime: true
thanks for taking your time to look at this

Answer 1

What's the problem?
You say that there are 15 prime numbers in the range 1-25. Your method printPrimeNumbers() prints the last calculated primes, and that is 15. So the program works.