How to find factors of number?

Question

I have a prime number program set up that finds prime numbers and to find two prime numbers beyond the number inputed. I also want to find the factors of the number inputed. I am brain freezed on finding the factors. For example I want to display 20 = 2 x 2 x 5, and for prime numbers I want to display 7 = 7. The factors will be displayed in label.
I already have the first factor, but how do you continue to add factors to the string, that is going to be put into the label? I think it is a for loop in a for loop but not sure how to work it out??????
here is my factor method
private void factor(long value)   //bring in number from user
          long firstVal;
          String output = value + " = ";
               for (long a = 2; a < 12; a += 1)
                    if (value % a == 0)
                         firstVal = value / a;
                         output = output + a + "x";
     }//factor-thanks

Answer 1

Well that was to illustrate the point so that the person asking question can take correct direction.
But you don't want to use your brain at all right.
Then here is the code
import java.math.*;
import java.util.*;
public class DirectSearchFactorization {
  private long max = 0;
  private Vector trialDivisors = null;
  private long nDivisions = 0;
  // Constructor
  public DirectSearchFactorization (long max) {
    this.max = max;
    // The trial divisors include all primes <= sqrt (n).
    // The trial divisors must also contain at least one
    // value such that d(k) >= sqrt (n).
    int sqrtn = (int) Math.ceil (Math.sqrt (max));
    trialDivisors = SieveOfEratosthenes.getPrimes (sqrtn);
    trialDivisors.addElement (new Long (sqrtn));
  public long getNumDivisions () {
    return nDivisions;
  // Get prime factors
  public Vector getPrimeFactors (long n) {
    if (n > max) {
      String s = n + " > " + max;
      throw new IllegalArgumentException (s);
    Vector factors = new Vector ();
    nDivisions = 0;
    // Step 1
    int k = 0;
    long divisor;
    Long divisorObj;
    long quotient;
    long remainder;
    // Step 2
    while (n > 1) {
      // Step 3
      divisorObj = (Long) trialDivisors.elementAt (k);
      divisor = divisorObj.longValue ();
      quotient = (long) Math.floor (n / divisor);
      remainder = n % divisor;
      nDivisions++;
      // Step 4
      if (remainder == 0) {
        // Step 5
        factors.addElement (new Long (divisor));
        n = quotient;
      else {
        // Step 6
        if (quotient > divisor) {
          k++;
        else {
          // Step 7
          factors.addElement (new Long (n));
          break;
    return factors;
import java.util.*;
public abstract class SieveOfEratosthenes {
  public static Vector getPrimes (int upTo) {
    int size = upTo + 1;
    boolean [] flags = new boolean[size];
    Vector primes = new Vector ();
    double limit = Math.sqrt (size);
    // Set flags
    for (int i = 2; i < size; i++) {
      flags[i] = true;
    // Cross out multiples of 2
    int j = 2;
    for (int i = j + j; i < size; i = i + j) {
      flags[i] = false;
    // Cross out multiples of odd numbers
    for (j = 3; j <= limit; j = j + 2) {
      if (flags[j]) {
        for (int i = j + j; i < size; i = i + j) {
          flags[i] = false;
    // Build list of primes from what is left
    for (int i = 2; i < size; i++) {
      if (flags) {
primes.addElement (new Long (i));
return primes;
User Interface
import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;
import java.util.*;
// The applet tests the DirectSearchFactorization class
public class FactorizationApplet extends Applet {
private Button factorButton = null;
private Label numberLabel = null;
private TextField numberTextField = null;
private Label numDivisionsLabel = null;
private TextField numDivisionsTextField = null;
private Label factorsLabel = null;
private TextField factorsTextField = null;
private DirectSearchFactorization dsf = null;
private static final long MAX = 500000;
// Override Applet methods
public void init () {
Panel panel = new Panel ();
panel.setLayout (new GridLayout (3, 2));
numberLabel = new Label ("Number to Factor <= " + Long.toString (MAX));
panel.add (numberLabel);
numberTextField = new TextField ("387921", 25);
panel.add (numberTextField);
factorsLabel = new Label ("Prime Factors");
panel.add (factorsLabel);
factorsTextField = new TextField ("", 25);
factorsTextField.setEditable (false);
panel.add (factorsTextField);
numDivisionsLabel = new Label ("Number of Divisions");
panel.add (numDivisionsLabel);
numDivisionsTextField = new TextField ("", 25);
numDivisionsTextField.setEditable (false);
panel.add (numDivisionsTextField);
add (panel);
factorButton = new Button ("Factor");
add (factorButton);
dsf = new DirectSearchFactorization (MAX);
public void paint (Graphics g) {
public boolean action (Event e, Object arg) {
if (e.target == factorButton) {
factor ();
repaint ();
return true;
else {
return false;
private void factor () {
long n = 0;
factorsTextField.setText ("");
try {
n = Long.parseLong (numberTextField.getText ());
if (n <= MAX) {
Vector factors = dsf.getPrimeFactors (n);
factorsTextField.setText (factors.toString ());
numDivisionsTextField.setText (Long.toString (dsf.getNumDivisions ()));
} catch (Exception e) {
System.out.println (e.toString ());
// Run as application
public static void main (String[] args) {
// Create frame to house the applet
Frame frame = new Frame ("Factorization into Primes");
// Create an instance of the applet
FactorizationApplet app = new FactorizationApplet ();
// Add it to the center of the frame
frame.add (app, BorderLayout.CENTER);
frame.setSize (450, 150);
// Listen for window closing event
frame.addWindowListener (new WindowAdapter () {
public void windowClosing (WindowEvent e) {
System.exit (0);
// Call the applet methods
app.init ();
app.start ();
// Set the frame visible
frame.setVisible (true);